Wellingtons would make a good Crassus proxy, which lists use these again? It'd have the benefit of an armoured roof but would carry only 35 troops (7 stands). I plan to glue two of them close together on a base and count it as a single Gorgon.
Gladstonian's could be good proxies for a
Dominus, which unusually has 40k rules but no model. It has 3 Bombard mortars on top (6BP ignore cover slow firing) but can only fire one if it moves that turn.
I have hazy memories of E&C producing an AM list including these vehicles and more regular IG tanks than the current Skitiarii list, but I don't know if it got any playtesting at all. Maybe it was one of the lists in E&C's sadly unfinished epic supplement which the community didn't seem to be motivated to work on?