I went through much the same drill when I was told putting a '68 Pontiac 400 engine into my '57 GMC V-8 truck was a "bolt in". well,it WAS,except for the flywheel,clutch,clutch linkage,bellhousing,carb linkage,generator mounting,heater hose locations and starter.But now that I have it all worked out and it runs great,I've decided to look for a 270 to install instead.Anybody have a good running 270 to trade for a good running 400 w/fresh AFB?
Glad your project worked out well.
Speed

1954 GMC 350
1957 GMC 1/2 ton
1962 Chevy C-30
1952 Chevy 6400 dump bed project truck
'98 Harley FLSTC
'66 Pontiac Catalina
'76 Chevy 1 ton Duallie
'84 Bronco II
'78 Dodge W-200
'81 Toyota 4X4 truck