Big Block AD's look here

[mr48chev]

I think it has more to do with where you set the engine in the truck.

I put a lot of miles on the 48 with a 283 bolted to a 50's/60's V8 truck bellhousing which bolted to the stock center crossmember. No real clearance issues except for the exhaust and steering box thing. It was pretty tight on the firewall with that setup. I don't think there would be room with a bigblock to do it without modifying the firewall to clear the heads.

When I subframed the truck and put a 350 with Turbo 400 in it I had the master cylinder and booster on the firewall but it was a big ugly zit on an otherwise clean firewall and I don't intend to do it again.