I'm glad the comparison is helpful! My prior experiences with spacers were only with small block Fords and Chevys with aftermarket cams so it's kind of an apples-to-oranges comparison, but since I had both it was a fun experiment.

I've read about the 428 CJ regrind and a place called Oregon Cam Grinders, but I feel like I'm already pushing the limits of the stock chassis and I'm sure you know how that can snowball. Winding it out in third I'm hitting about 65mph and hitting fourth just catapults it from there—that's good enough for me currently and probably much faster than this truck was originally designed to go anyway.

eBay sometimes turns up a rare gem and recently I stumbled across a set of early intake manifold keepers. They were incorrectly listed as being for Edsel exhaust manifolds so I'm happy I found them at all! After cleanup and some paint I snapped a photo comparing them to the late keepers for reference. The length is significantly different and it amazes me that I was able to use late style keepers at all with the early intake.

Is that a 1/2" difference in widths? Thank's again for posting that.

The early style is about 3" long, the later style is roughly 2.25" so the difference is about 3/4". Width was the same however.

So what does this manifold belong to? It was in the trunk of the parts car (1960 Montclair) that I bought. C3VE 9425-D

C3VE 9425-D sounds like a 63-65 intake. I believe that's what was on my motor before I swapped it out for the earlier manifold.