Tire size for my scamp

Additional note:
When searching the tire size, include results for '67+ Dart (not Dart Sport). Same rear wheel wells and fender openings as a Scamp.
You should be able to go 225 70 in the rear (235 may physically fit, but you're going to run into issues with speedometer calibrations); but I wouldn't go over a 215 70 in the front on stock rims at factory ride height.