The “other fabrication” that must be done for the booooring SBC swap is pretty much everything. Also be aware that you’ll be adding a couple of hundred pounds directly over the front wheels. Yeah, it’s been done, but don’t kid yourself that by the time you custom fabricate new mounts, a larger radiator, new exhaust, new trans tunnel, new driveshaft, etc, etc, that it will be any less expensive.
Frankly, the 215 with E-brock carb in my 62 is the most reliable car I own – it starts reliably and works perfectly despite the fact that I don’t drive it regularly. If you want a larger engine, get a 4.6 liter Rover. It is externally identical to the 215 (including the oddball bellhousing bolt pattern) and bolts into a 61-63 Y-body.