I have several sets of those heads.
I am pretty sure no water near there = But
it does not hurt to Sonic test them.
I would not be concerned with taking .250 off them
but could it not come off of the manifolds at least part of it
That's the catch, at this level ...they expect you have some headers.
I'd grind as little as possible and look at stacking gaskets, percys, a thin header flange by itsel and thin gasket on each side.
If I was intent on using those 340 hp manifolds.
Nope. Only reason I went aluminum was because it’s my daughters car and I wanna make sure it doesn’t overheat i.e. better cooling and that it doesn’t detonate i.e. I get a nice 0.035 quench plus it removes about 50 pounds of weight. that’s the only reason I want aluminum on the other daughters Duster and it’s worked out perfectly Car can run the AC all day and 110 and run perfectly cool, doesn’t detonate with spark advance that the engine really wants. None of my cars of really ever been over probably 3500 RPM.Aren’t you concerned about port mismatch using those manifolds with those heads?