BB 915 head valve size

Is there any reason not to use 2.08/1.74 valves vs 2.14/1.81? I am stuck with factory exhaust and 6bbl intake so would bigger valves actually hurt? I need to buy valves and have seats cut on a serdi so cost is not an issue, pistons have reliefs and are .001 in the hole. Heads are 79cc now, .039 head gasket. Intake side gasket matched, pushrod pinch is .080 wider, and will minor blend below the serdi cuts, and widen a little beside the intake guide. I put the heads on the block and scratched the cylinder wall edge on the head, and feel the bigger valve will not do much good on this engine. I also must use a streetable cam, nothing crazy.

Put the bigger valves in now, the 915 heads could have came with either 1.60 exhaust or the HP head size on the exhaust with 1.74.
Go with bigger on both and have the shop machine match the bowls to the new seats You can never have to much airflow

These are the 1.60, so at minimum the 1.74 exhaust need to be done.

Another way to go is to cut the 2.14 intake valves to 2.10-2.11.More costly but you won't shroud the int valve so much. Also you can put the valve at original height in the cyl head. The more the valve is sunk the less the flow. 1.75 exh valve will work fine.A little bowl work will help alot. I do this on the smaller bore engines and have had very nice results.Also saves heads from seat inserts.

If a decent amount of blending(by someone who knows what they're doing) isn't part of the plan with the addition of the big valves, then I'd recommend sticking with the stock 2.08/1.74 valve sizes.

I put .100 long-2.125 sb chevy intake valves in mine. They also had 5/16 stems. Exh was 1.80 ford 351 cleveland with 11/32 stems. If you are installing new guides you can use any stem size. Smaller means less weight. Engine made over 650 hp at only 10.5 to 1, on a 449/383 engine--4.28 bore x 3.900 stroke. 9.02 at 150mph 1/4 mile-in 2500# car.