Howdy Slade and All:
If you're already doing a performance valve job, then by all means go with the 1.75" intakes. The three angle valve job will make the biggest difference over the factory one angle seat and valve cut. Next in value would be to smooth the transitions from milled to cast surfaces in the valve pocket. Then, a 4th back cut angle on the port side of the intake valves. And then spend some time smoothing and polishing the chamber.
For your purposes, a 1.75" intake and a 1.38" exhaust is pretty good. This exhaust is 78% of the intake size, which is pretty good. Any larger size valves in an engine with a bore this small would see marginal returns and mainly at higher rpms and at highest lifts. With the 3.68" to 3.72" bore it is very difficult to realistically (in terms of money and value in return) get bigger than 1.75" intake and 1.5" exhaust.
For street and general use, we don't back cut the exhaust and leave the margin a little wider, at .100", to help with heat transfer to the head. We've used 144 1.467" intake valves as exhaust valves with good results, so far. We have shunned 1.5" chevy valves because of the extra machining required to get them to fit, and because of the small bore and inherent shrouding. Milling will help to unshroud, by dropping the valve a little deeper into the cylinder.
Cutting the head to accomodate a 1.75" intake is not a big deal and should not cost an additional $100.
Anlushac11- I'd sure like to know a source for a 1.75" small stem Stainless Steel valve to fit our sixes? Please let me know where to find it? I had heard that Clifford was getting stainless steel intake and exhaust in 1.88" and 1.50" from SSI, but have had no luck in finding since Eric parted with Clifford. If we could source these valves direct from SSI it may be a feesible option.
Adios, David