The zx L28 block should have F54 cast into it. The '81-'83 F54 block with
P90 P79 heads have the flattops. Naturally if rebuilding it you don't want old used pistons but a fresh 20 or 40 over bored block with matched oversize pistons. Hone and ring is a poor way to rebuild as there is ALWAYS ring wear at TDC.
The head cc says everything about compression. But not saying much as... "I am running a earlier model head on the block as well." well what earlier head? E31, E88, N42? .... E88 heads are the same combustion chamber size as the '75-'78 N42 and N47 280z heads. The '77 and up 280 N47 head has hardened steel valve seats replacing the softer bronze ones that relied on leaded gas to lubricate.
Some guesses and some math.... 42cc combustion chamber? and flattops makes 10.366 compression, slightly more when over size pistons used. Stock is 8.66?