Help on 408 build

Well, unless the heads have been milled substantially, it’s not 13:1.
Typical stroker flat top piston, zero deck clearance, .040 gasket.......even with the heads as small as 60cc works out to only 12.14:1.
(13:1 would require a 54.5cc head)
If you added 10cc worth of gasket(19cc total) it would drop to 10.83.
That’s if the heads were as small as 60cc.
If the heads were a more “normal” 65cc, it would drop to 10.28.
69cc, it would drop to 9.89.

Zero deck, 5cc pistons, the .098” Cometic gaskets, 64cc heads...... puts it at 10.08.

Add some cam duration and you’ll be a lot closer to pump gas operation(might need octane boost for WOT operation).

My suggestion is pull a head off and get some measurements before you order any parts.