I'm actually watching a throttle body w/ adapter from an '89 GMC 454 on
eBay right now.
My only concern was that it doesn't split into 4 distinct holes for the
manifold, it just mirrors the outer shape of the carb's bore pattern.
Wouldn't air flowing straight down and hitting that 'wall' in the
center of the bore cause some sort of problem?
My manifold has 4 holes, 2 smaller ones for the primaries, and 2
biggers ones for the secondaries, which is the way all the Quadrajet
manifolds I've seen are.
When I was shopping for the adapter to put the Edelbrock (AFB) on the
manifold, I found 2 different types. The 'open' type, which takes the
square bore and opened it up to match the Quad pattern, was cheaper and
that's what I bought. Then after I bought it I found one that in my
mind was better. It actually had 4 holes in it that smoothly angled
away and got bigger to perfectly match the Quadrajet pattern. The
second type would have to be better for smooth, turbulence free
airflow, although I don't know how much of a difference it'd make at my
RPM range (rarely above 3000 I'm guessing, haven't hooked up the tach
yet). I suppose it might not really be a problem unless I was racing,
but you probably know better than me.