diff --git a/src/basic/engine_editor/find_line.s b/src/basic/engine_editor/find_line_38K_60K.s
similarity index 77%
rename from src/basic/engine_editor/find_line.s
rename to src/basic/engine_editor/find_line_38K_60K.s
index b99f86a2..8a52c25c 100644
--- a/src/basic/engine_editor/find_line.s
+++ b/src/basic/engine_editor/find_line_38K_60K.s
@@ -6,6 +6,8 @@
 // Find the BASIC line with number in LINNUM
 
 
+#if CONFIG_MEMORY_MODEL_38K || CONFIG_MEMORY_MODEL_60K
+
 find_line_from_start:
 
 	// Get pointer to start of BASIC text
@@ -24,13 +26,9 @@ find_line_from_current:
 	// Fetch the high byte of line number and compare
 	ldy #$03
 
-	// XXX consider optimized 46K/50K version
-
 #if CONFIG_MEMORY_MODEL_60K
 	ldx #<OLDTXT+0
 	jsr peek_under_roms
-#elif CONFIG_MEMORY_MODEL_46K || CONFIG_MEMORY_MODEL_50K
-	jsr peek_under_roms_via_OLDTXT
 #else // CONFIG_MEMORY_MODEL_38K
 	lda (OLDTXT),y
 #endif
@@ -46,8 +44,6 @@ find_line_from_current:
 
 #if CONFIG_MEMORY_MODEL_60K
 	jsr peek_under_roms
-#elif CONFIG_MEMORY_MODEL_46K || CONFIG_MEMORY_MODEL_50K
-	jsr peek_under_roms_via_OLDTXT
 #else // CONFIG_MEMORY_MODEL_38K
 	lda (OLDTXT),y
 #endif
@@ -69,15 +65,11 @@ find_line_next:
 	jsr peek_line_pointer_null_check
 	bcc find_line_fail                           // branch in no more lines exist
 
-	// XXX consider optimized 46K/50K version
-
 	ldy #$00
 
 #if CONFIG_MEMORY_MODEL_60K
 	ldx #<OLDTXT+0
 	jsr peek_under_roms
-#elif CONFIG_MEMORY_MODEL_46K || CONFIG_MEMORY_MODEL_50K
-	jsr peek_under_roms_via_OLDTXT
 #else // CONFIG_MEMORY_MODEL_38K
 	lda (OLDTXT),y
 #endif
@@ -87,8 +79,6 @@ find_line_next:
 
 #if CONFIG_MEMORY_MODEL_60K
 	jsr peek_under_roms
-#elif CONFIG_MEMORY_MODEL_46K || CONFIG_MEMORY_MODEL_50K
-	jsr peek_under_roms_via_OLDTXT
 #else // CONFIG_MEMORY_MODEL_38K
 	lda (OLDTXT),y
 #endif
@@ -103,3 +93,5 @@ find_line_fail:
 
 	sec
 	rts
+
+#endif
diff --git a/src/basic/engine_editor/find_line_46K_50K.s b/src/basic/engine_editor/find_line_46K_50K.s
new file mode 100644
index 00000000..cbcce444
--- /dev/null
+++ b/src/basic/engine_editor/find_line_46K_50K.s
@@ -0,0 +1,93 @@
+// #LAYOUT# STD *       #TAKE-HIGH
+// #LAYOUT# *   BASIC_0 #TAKE-HIGH
+// #LAYOUT# *   *       #IGNORE
+
+// This has to go $E000 or above - routine below banks out the main BASIC ROM!
+
+// Find the BASIC line with number in LINNUM
+
+
+#if CONFIG_MEMORY_MODEL_46K || CONFIG_MEMORY_MODEL_50K
+
+find_line_from_start:
+
+	// Get pointer to start of BASIC text
+	jsr init_oldtxt
+
+	// FALLTROUGH
+
+find_line_from_current:
+
+	// Unmap BASIC lower ROM
+
+	lda #$26
+	sta CPU_R6510
+
+	// Check if line is not empty
+
+	jsr peek_line_pointer_null_check
+	bcc find_line_fail
+
+	// Fetch the high byte of line number and compare
+
+	ldy #$03
+	lda (OLDTXT),y
+
+	cmp LINNUM+1
+	beq !+
+	bcs find_line_fail                           // branch if line number too high
+	bne find_line_next
+!:
+
+	// Fetch the low byte of line number and compare
+
+	dey
+	lda (OLDTXT),y
+
+	cmp LINNUM+0
+	beq find_line_success
+	bcs find_line_fail                           // branch if line number too high
+	bne find_line_next
+
+find_line_success:
+
+	// Restore default memory mapping and quit
+
+	lda #$27
+	sta CPU_R6510
+
+	clc
+	rts
+
+find_line_next:
+
+	// Advance to the next line
+
+	jsr peek_line_pointer_null_check
+	bcc find_line_fail                           // branch in no more lines exist
+
+	ldy #$00
+	lda (OLDTXT),y
+
+	pha
+	iny
+	lda (OLDTXT),y
+
+	sta OLDTXT+1
+	pla
+	sta OLDTXT+0
+
+	jmp_8 find_line_from_current
+
+find_line_fail:
+
+	// Restore default memory mapping and quit
+
+	lda #$27
+	sta CPU_R6510
+
+
+	sec
+	rts
+
+#endif
diff --git a/src/basic/peek_line_pointer_null_check.s b/src/basic/peek_line_pointer_null_check_38K_60K.s
similarity index 66%
rename from src/basic/peek_line_pointer_null_check.s
rename to src/basic/peek_line_pointer_null_check_38K_60K.s
index a73351d4..7f3457f4 100644
--- a/src/basic/peek_line_pointer_null_check.s
+++ b/src/basic/peek_line_pointer_null_check_38K_60K.s
@@ -5,40 +5,43 @@
 // Return C=1 if a pointer in BASIC memory space is NULL, else C=0
 // X = ZP pointer to check
 
+
+#if CONFIG_MEMORY_MODEL_38K || CONFIG_MEMORY_MODEL_60K
+
 peek_line_pointer_null_check:
 
-	ldy #$00
+	// Check the pointer
+
+	ldy #$01                 // for non-NULL pointer, high byte is almost certainly not NULL
 
 #if CONFIG_MEMORY_MODEL_60K
 	ldx #<OLDTXT+0
 	jsr peek_under_roms
 	cmp #$00
-#elif CONFIG_MEMORY_MODEL_46K || CONFIG_MEMORY_MODEL_50K
-	jsr peek_under_roms_via_OLDTXT
-	cmp #$00
 #else // CONFIG_MEMORY_MODEL_38K
 	lda (OLDTXT),y
 #endif
 
-	bne ptr_not_null
-	iny
+	bne !+
+	dey
 
 #if CONFIG_MEMORY_MODEL_60K
 	jsr peek_under_roms
 	cmp #$00
-#elif CONFIG_MEMORY_MODEL_46K || CONFIG_MEMORY_MODEL_50K
-	jsr peek_under_roms_via_OLDTXT
-	cmp #$00
 #else // CONFIG_MEMORY_MODEL_38K
 	lda (OLDTXT),y
 #endif
 
-	bne ptr_not_null
+	bne !+
 
 	// Pointer is NULL
+
 	clc
 	rts
+!:
+	// Pointer not NULL
 
-ptr_not_null:
 	sec
 	rts
+
+#endif
diff --git a/src/basic/peek_line_pointer_null_check_46K_50K.s b/src/basic/peek_line_pointer_null_check_46K_50K.s
new file mode 100644
index 00000000..c837cfe9
--- /dev/null
+++ b/src/basic/peek_line_pointer_null_check_46K_50K.s
@@ -0,0 +1,46 @@
+// #LAYOUT# STD *       #TAKE-HIGH
+// #LAYOUT# *   BASIC_0 #TAKE-HIGH
+// #LAYOUT# *   *       #IGNORE
+
+// This has to go $E000 or above - routine below banks out the main BASIC ROM!
+
+// Return C=1 if a pointer in BASIC memory space is NULL, else C=0
+// X = ZP pointer to check
+
+
+#if CONFIG_MEMORY_MODEL_46K || CONFIG_MEMORY_MODEL_50K
+
+peek_line_pointer_null_check:
+
+	// Unmap BASIC lower ROM
+
+	lda #$26
+	sta CPU_R6510
+
+	// Check the pointer
+
+	ldy #$01                 // for non-NULL pointer, high byte is almost certainly not NULL
+	lda (OLDTXT),y
+	bne !+
+	
+	dey
+	lda (OLDTXT),y
+	bne !+
+
+	// Pointer is NULL
+
+	lda #$27
+	sta CPU_R6510
+
+	clc
+	rts
+!:
+	// Pointer not NULL
+
+	lda #$27
+	sta CPU_R6510
+
+	sec
+	rts
+
+#endif