The 340 and 360 intake ports on the heads and intake manifold are larger than the 318 heads and intake ports which will cause reversion
That is really a non-issue except in a max effort engine build and you wouldn't being doing that to a 318 anyway. I don't know why people keep bringing that old chestnut up, got any dyno pulls to prove it is an issue?
All that said, I ran the factory spreadbore intake on my otherwise stock 87 2bbl 318, yes the small port heads with zero reversion issues. Ran an Edelbrock 1406 carb on it without an adapter. What I did was run a thick (~3/8") carb base gasket. Don't have a PN though, I just picked it off the shelf back when there were speed shops and carb mounting gaskets to look at. Might look at Edelbrock Carburetor Adapters 2732, it's about as thin an adapter as you will see, probably thinner than my thick gasket trick.
You will also need the kickdown linkage addressed as the 2bbl stuff doesn't play so well with a 4bbl, did you get the adapter for the throttle and kickdown linkage as well?
