Z head and O head on 1973 340

I have a 1973 340 4 speed Duster that has a # matching engine and transmission. I would think with a car that still has a matching drivetrain the heads have a good chance of being what came on the car.

The O head has 341891 B (5 is not cast) and the Z has 3418915. The O also has 360 cast into it. However, in 1973 the 340's had 3671587 heads but this doesn't mean the engine couldn't have got some 1972 348915 heads.

From the information I've seen these should be 1.88/1.60 valves. The rockers are 273. Are these heads going to perform amazingly better if I took .040 off the surface and put 2.02" intake valves in? The cam is 224/224 @ .050 and lift is .468. Would there be piston clearance issues by milling the heads? Different head gasket thickness takes care of that, right?