We had a 2.250" intake and a 1.800" exhaust in our heads with stock valve location. Very close together. So much so that on nitro and at high RPM's due to the large stem to guide clearance required, they hit each other. We reduced the exhaust head diameter and increased the stem diameter to 3/8". Problem solved. Normally aspirated, 2.250/1.80 would work OK even with a 5/16" intake stem, but I wouldn't build a max effort engine with those sizes. I would think a larger intake and slightly smaller exhaust would be a better choice, which is probably what Mike chose. Good luck on the dyno.
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