I’m getting ready to build the frame on my 51 and it has a mustang II front end. I’m planning on using a 350 only because i have one lying around. Do you have pics i can see? D8AF7DAA-E4D1-491B-B014-D4F7F08F77A4.jpeg
You will need to address the center crossmember. It will likely be in the way of your transmission. Even if it isn't, you will have trouble if you ever need to pull the transmission later on. I cut the middle of of mine, welded drop plates to the stub ends of the remaining ends which are riveted to the frame and welded plates to the ends of the removed center section, and drill holes for bolts so that I could bolt the center back on leaving it about 2 inches lower than it was.