Do you know the casting number on the heads? The 416’s were decent for their intended application (305) and if you have these heads and they’re all cleaned up and ready to go – they’ll suffice. If they’re stock, they have 1.60” or 1.84” intakes and 1.5” exhaust valves. If they’ve been modified, there’s a high probability that someone installed 1.94” valves – making them very similar to the old “Camel Hump” heads but with shorter runners. The bigger intakes help on the fuel side but there’s only so much that can be done for overall flow and you’ll not come close to a set of stock Vortecs that are readily available and you won’t have to wonder if they’ll perform. These are also a thin wall casting and if machine work has been done you’ll want to magniflux the heads to make sure they’re not cracked. The head will ever-so-slightly cover the bore as they’re meant for a 3.736” bore opening versus the 4 inch 350.

If you do decide to use the 305 heads, check clearances very closely and know going in that they have small intake runners and 58cc chambers – higher velocity but less total volume. While the 58cc chamber will up your compression ratio, it can also cause problems with flat top pistons so I’d go with a dished piston. The 58cc chambers and the dished pistons should get you somewhere in the 9.4-9.6:1 compression ratio on a non-milled head (depending on gasket thickness) but you shouldn’t have to worry about valve-to-piston clearances.

Keep us in the loop and have fun
Glenn