It takes some work to get a Mopar big block valvetrain to work at 0.800 lift.

My advice is to buy one each of several different retainers and locks. Measure each of them and keep the numbers in a notebook. The mfg numbers cannot be trusted, you have to measure them yourself.

You should be able to find valve springs that will handle 0.800 lift at less than 2.100 installed height. Maybe 2.050 or even 2.00 if you look hard enough.