The 85 intake manifold won't work with the 90 heads, so you will need to purchase an aftermarket intake if you want to use a carburetor or use a 87 to 95 intake if you want to change over to TBI.
yes
350 heads will bolt to the 400 block. They will need to be drilled for the "steam ports" in the 400 block.
a 350 is a small block those heads will fit on and Chevy SMALL block not a big block
Yes , but you will need a tbi intake to fit vortec heads if you retain the 90 TBI fuel system.
yes, you can use those heads. the block does have small changes to it but no problm will occur
lt1 is a 350
The strength of the engine block The 72 would be a better / stronger block.
Yes their the same block....
yep
NO......
The 1990 block would have the integrated one-piece rear main seal. Oil pan and crankshaft are not interchangeable.
the heads should fit as long as your not trying to put them on a big block