From my experience.
Wc51 has way too much utility for such a cheap unit regardless doctoral or not and can be quite oppressive in comparison to other ultra lights.
I would defiantly start by removing the artillery and mayby Mark target, their isn't any reason for it to have those. I know this wouldn't make too much sense, but also remove the ability to carry troops after upgrading.
Calv rifle men are decent, after the t Thompson upgrade you can still equip them with a bar but honestly they are still fine without it.
Combined arms from my experience is a criminally underrated ability. I haven't seen anyone even in streams ever use it when they could.
As for the 76mm, works extremely well against tier 3 wher, beyond that it falls flat (unless its vet 3).The bulldozer blades up-grade makes up for it through.