65 273 Intake manifold

You do realize that the intake manifold bolts on a '65 are at a different angle than on the Performer, which is designed for the different '66 and later bolt configuration?
As far as the ports go, I would wait and see what the manifold looks like when you get it. You may want to clean up some of the casting imperfections, but I would match it up to the heads with an actual 273/318 intake gasket (not the 340/360 sized gasket- because since you didn't say, I'm assuming we're dealing with a '65 273 motor) and maybe do a little gasket matching. But, it's a moot point if it's a '65, since the manifold won't fit. Start looking either for some '66 and later 273/318 heads, or a Commando/Charger or old Eddy D4B 4bbl. manifold to fit your '65 heads.