What's the difference?

Put an adapter on it to go from the square Holley pattern to the spreadbore pattern the manifold has. If you arent worried about exhaust heat in the manifold you can weld the egr passage shut or most gasket kits have a metal insert to plug them off... the removable plate on the topside of later mamifolds like yours can be blanked off with a fabbed plate or you might find the block off on a junkyard manifold. Found on both 2V and 4V intakes.
It might have the offset water neck which is handy (and nesessary) to use the later smaller AC compressor... I think only the Performer (not RPM or Air Gap) is the only aluminum 4V manifold to have this. FYI.

Trivia... the best flowing spreadbore stock manifold is the 1971 manifold.. this has the casting number 3512100. Stocker class drag guys supposedly used to pay extra for these. The 71 340 was the highest NHRA rated 340 short of the TA/6 Pak.. it had high compression and this manifold with the T-Quad..used to be NHRA factored at 310 or 315 HP opposed to the 68-70 340's factored to 300.
if you want to go aluminum, the non air gap Performer, the Wieand Stealth, or any dual plane manifold can be "sleeperized" with a good coat of paint.. if you are really dedicated, mill or grind off the brand name!

Paint the whole thing black, lie like a rug and tell everybody you yanked the engine out of a 1984 pickup.. they were black by that time..and hide the carb under a big stock air cleaner with a bunch of air holes drilled where they don't show...

That would make a good thread all it's own...