Will a 1976 Aluminum 1 Barrel carb work on my 69 Slant 6 225

Good goats! Your imaginations and keyboards are running away with y'all. A '76 aluminum intake is not the potentially porous 2-piece casting. There is no choke incompatibility caused by swapping one 1bbl intake for another 1bbl intake on a Slant-6, ever. There is no such thing as a '76 aluminum intake "without exhaust passages". There is no (for cryin' out loud) carburetor jetting issue caused that way, either—don't let's be making up ghost stories in response to a legitimate question, eh? The one and only issue is the presence of an EGR valve mount pad on the '76 intake. This is easily solved by either putting on an EGR blockoff plate (cheap and easy, as previously described) or installing an EGR valve rotated 180° from its normal position. Either way, use a fresh EGR gasket.

Beyond that, as is the case with any manifold R&R on a Slant motor, it is very much worth your while to get the good gaskets for the manifolds-to-head and intake-to-exhaust junctions.

(And yes, the aluminum intake is worth having if it's in the house. Sure, the weight reduction is a thing, but the better cold-engine driveability is a bigger and nicer thing, and the small fuel economy improvement adds up in dollars over time)