I have a 350 in my rig, but the motor mounts are terrible, just stock ones from a truck welded on. I want to move to something smaller, more secure, etc and I think I may have found something interesting:

http://store.summitracing.com/partdetail.asp?autofilter=1&part=TRD%2D4195&N=700+4294861902+115&autoview=sku

These are really small and snug and I think they would work great for my motor. I was wondering though .. does anyone know how wide the frame rails are on the older Bel Airs? Do you think it's similiar to a Samurai? If so, then I could make subtle adjustments to these to get them to work ...

well, when I put my 4.3 in, (don't have it yet), I'll probably make some mounts that look like a spring eye with poly bushings. I hear those work great. just a bracket with flanges on one side(sort of like the frame mounts flanges), and a tube with bushings in it for the other side.