The '74-'75 heads do have exhaust valve seat inserts from the factory, not just induction hardening.

The K-jet head are the same casting as the D-jet F heads, but not the same as the E heads, so possibly there's more to the compression difference than just thickness. It's not difficult to drill and tap the K-jet heads to accept the D-jet aux air valve and coolant temp sensor.

Part of why the E engines are higher compression is that the head gaskets were nominally .030" thick, vs. .050" for the F. These are NLA -- the .050" is now sold for all injected B20s. I use the B20B gaskets, which are advertised at .030" (they actually crush to about .034"), even though the fire rings intrude very slightly into the wider combustion chambers on the E/F heads. I have not had any problems with that.

The advertised compression numbers assume that the pistons come up even with the block deck, which they don't. They vary somewhat (even within a particular engine), but they're usually down at least .020". I would deck the block so they do come up to zero deck height, or even .002" above. You can mill down the crown of the taller piston/rod stacks to make them all even.

Because the E and F castings are different, I can't tell you exactly how much to shave off. The chamber volume on the E head are about 47 to 48cc, so if you take off enough to get that, you'll have the E compression, assuming stock bore diameter.