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You don't port an engine to a bigger displacement.
That aside, yes something that fits a 350 should fit a 383, with certain exceptions.
I would suggest some homework.u
All that should matter are what heads are on it, making sure the headers fit if you have non-stock angled spark plugs, and matching the port size to the headers so you don't create a restriction.
Do you want the stock appearance '69 sidepipes, or the Doug's/Hooker style?
It appears to me the OP has a built engine, so why not go for the best? Probably has a better drivetrain, suspension, and tires for the built engine. In the overall scheme of dollars spent, it isn't a lot.