"Most" non Hemi motors are .040-.050 in the hole... That is why they sell the .040 longer Rod. Put a Hemi flat top in which has a .020 shorter comp. height and that puts it .020-.030 in the hole... Put a thin .009 gasket on and things are good...
NR racing sells a flat top with the same comp. height as the dished piston... That will leave you either flush or .010 in the hole... Put a thick .040-.045 gasket on and you are good to go...
The .020 Rod is mostly for the Hemi predator because "most" Hemi are .030-.020 in the hole...
I like the .040 Rod in the Hemi if it is .030 in the hole leaves ya with .010 pop up... Use a .045 gasket and life is good...
Many ways to have fun and build them...
One that I like to run... is a Non hemi block , with a Honda crank, Hemi flat top a Honda 3.403 Rod leaves it .010 pop up and a .045 gasket, Isky .310 cam, 1.3 rocker intake 1.2 rocker exhaust, 14cc head with a 28.5mm intake valve and a 25mm exhaust valve, 348 Tilly on meth... Hauls the mail... But the block is well braced and checked often for cracks...