The late 248s had a 6-bolt crank flange pattern so you "should" be OK there.
The 302 had a couple of different front motor mount setups. There was a big "horse collar" mount that bolted to frame somewhere, and some allegedly used side motor mounts like a V8 though I've never seen an example. 302s came in a lot of big GMCs like busses and commercial chassis, and many others in military vehicles. They never came in pickups, thus the front motor plate behind the timing cover is just a flat piece of steel, it won't have the angled central motor mount like the 248 has. The 248 plate is a bolt-on, but beware of interference with the front damper pulley, if you use the stock 302 double groove pulley. You can turn down the rear face of the pulley for clearance, or change the whole balancer out for something more compact. Even though the engines are the same dimensions, the 302 took up more room due to the accessories. But in general it is pretty straightforward swap.
