Ironhead Swing Arm

Building a Ironhead bobber with a 79 mtr with S+S 1200 Stroker , Andrews Cams Big Valve Heads, anyway just found out the motor won't fit in the right side shift frame with out major modifications and really feel bad about cutting up that frame. So my question to the group will a early 70's swing arm fit on a late 70's frame?

Thanks,

Kurt