340 build

You need to look at the bottom of the piston, there may be some variations in thickness to be aware of.
The first step is to call the manufacturer and see how much is safe to be removed.
I like you plan but if you remove two much, and you loose a tight quench........well you have shot yourself in the foot, so to speak.
a .040 head gasket is common and inexpensive.
shave .010 to .015 of the piston and now you're .020" piston goes down to .005 -.010 above deck. have the block decked. you low deck hole(.020) will lose deck height by at the most,.002"(ask you machinist i'm only guessing)

#1 call manufacture of piston and ask how much can be removed safely
#2 Verify that the tallest piston is .020 out of the hole(Remember, .002" makes a hug different in you planning)
#3 find out from machinist how much will have to be removed from the lowest spot on the deck (it my only be a half of a thousand aka .0005"
Note: AJ/Forms said that he had run as tight of a piston to head clearance a .023" without any head to piston kissing!!! Keep that in mind as you figure this all out.