Very welcome. If it were me, I would drop the slant six with the K frame and trans, then put a V8 K member in and drop in a newer magnum as they are plentiful and already have a roller cam. I'd run EFI on it and enjoy the car.
70 Challenger RT 440-6, 73 Cuda (under const)
05 Durango, 99 Dakota, 01 Ram 4x4, 14 2500 4X4, 10 PCP Challenger RT, 01 Viper GTS ACR, 52 B3B w/330 Desoto Hemi, 70 Hemi RR, 61 Jeep FC170
9 x Challengers. AAR Cuda, 4 RR, 2 GTX, 4 Chargers, etc... (too many to list)