Next question, intake

[WyoRoadDog]

That was my thought as well, that the open port vs. split seemed like an advantage. I'm no engineer, but it seems to me having access to a larger volume of air/fuel mixture in the open port compared to the split port could only help mixing and amount that could actually be pulled in to the cylinder. It seems the most restrictive part then would be the head and intake valve, and not those PLUS the intake manifold channel.
I guess i'll be cleaning and painting that 351 manifold... and looking at the 500cfm carb.

[bigblockv6]

If you're going to be running A 500cfm Holley 2bbl there is no need what so ever for the Magnum manifold whether it's from a 351E or any larger Magnum V6. The discussion for using the larger Magnum manifold was for a 4bbl conversion, furthermore adapters are no longer being manufactured to install a 500cfm carb on Magnum manifolds. Your present 305 manifold only requires a Mr. Gasket #1937 adapter to use the Holley carb, it's a simple bolt on installation.

[TJ's GMC]

What Pete said. I do have a 4 down to 2 adapter that will work on a 305e and should work on a 351M manifold, but the results are rather a waist of time. I tried it and felt a little difference, but had I cleaned and rebuilt the 2 barrel it probably would have been the same. haha Not until I got a manifold and actually opened up the plenum did I notice much. But that's with a 4 barrel....two barrel doesn't really Need a manifold mod. Like said, if you do a 500 best to get an adapter and put it on. The 500 mod is the most common...I think 3/4 of the v6's here have it!

[bigblockv6]

The other thing is with the 305 manifold you can free up the restriction by opening op the base hole of the manifold with a die grinder to match the larger diameter throttle bores of the 500.

[TJ's GMC]

Originally Posted by bigblockv6

The other thing is with the 305 manifold you can free up the restriction by opening op the base hole of the manifold with a die grinder to match the larger diameter throttle bores of the 500.

I'd try it, but it would be a down grade from the 4 barrel.