I know exactly what you mean about wide spotting it at the gasket surface. Porting mistake #1, and why I did not touch the gasket side of the port outside of smoothing casting bumps. But now knowing the port's cross sectional area (2.34 sqin)is less than that of the intake valve minus stem (2.80 sqin), and the area from seat to valve at full lift is 2.64 sqin, the air is going to slow down from the gasket surface to the valve if I do nothing. So if I at least taper the port to the gasket now, and make a good showing of it on the stock intake manifold, it'll set me up well for the sheet metal intake, though the sheet metal intake is for the turbo engine, I expect the ports to be cleaned up to the standard gasket size.

Worse case the runners from the sheet metal intake have to be re-done, and I hardly expect to make a great intake on the first try, so may as well get a practice one in that can taper properly from plenum to valve.
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Rebuilding an OHC Pontiac 250 with EFI and a Turbo