I've built the Monogram and AMT Challengers, both are pretty straightforward. You are right about the 340 being vastly out of scale, it's almost as big as the 440 in the 70 GTX kit. The good thing is that the Hemi from the 71 Cuda and the aforementioned 440 are easy swaps. The AMT kit seems more true to scale and is an equally easy build, the only drawback is having to glue the top on for a hard top version.