Pfister Roman Tub replacement

[Mirmium]

Trying to replace our old pfister Roman tub faucet (unsure of model but home was built as a community “model” home in 1995. See pics. The handles go on well but then won’t screw because it seems these handle stems/valves (not sure what they are called) are not wide enough to catch the handle to screw tight. The faucet piece won’t fit as you can see it needs to be super narrow (almost like just a pipe) versus the wide piece there - able to get one Allen screw out but piece won’t come off. Any ideas? Thought replacing with a Pfister would make it easy like it was with the shower due to the valves