No I shouldnt have to notch the frame in the rear...its not going to be that low... I think

...I may have the notch the rear crossmember so the pumpkin doesnt hit....but I think the axle tubes should be fine
As for the k-frame design....the RMS (and the other 2....Magnumforce and XV) is really designed for "less aggressive stance" of a car...i.e not running 19 inch front rims and 20 rears.....not shooting for the total "in the weeds" look etc. It has a much bigger market of the "average guy" thay just wants to get rid of the 30 year old torsion bar style suspension in the Mopars...plus there are just fewer guys cutting up Mopars and doing wild stuff... their numbers are growing but not nearly as many as Chevy and Ford etc.
So I cant fault RMS for staying more "in the middle of the road" for their design