The subject says it all. I have an ancient Lionel loco , #2020, PRR 6-8-6 that runs in conventional mode only. Perhaps ERC can upgrade it to TMCC _ I don't know. But does Lionel currently make any such smaller locos that can be run with their Legacy system? I'm not interested in any Lion Chief versions. I think that MTH makes the RailKing line that is the smaller size and I believe that Legacy can control the MTH locos after a fashion but I'm not sure.
Dan
To the best of my knowledge:
1) There is probably an ERR upgrade that would fit your engine, making it have TMCC (not full Legacy) features, which are fully controllable with the Legacy command base/remote since Legacy is fully backward compatible to run all TMCC engines.
2) Yes, but in a round about way. It was uncommon to see basic PW style pieces offered with full Legacy features. There could be exceptions I'm not aware of, but in general, I don't think they offered classics like a Post War clone 726 Berk or 681 Turbine with full Legacy features.
Side note: those are just just 2 examples - note that many (maybe almost all) of these PW classics were offered with TMCC around 15-20-ish years ago when TMCC first came out. The Century Club I and Post War Celebration lines specifically were designed to look like PW engines (with perhaps some minor upgrades, but essentially very close to PW style), but with TMCC electronics.
However, with the release of LionChief Plus 2.0 engines (not original LionChief, nor the previous LionChief Plus (no 2.0 after it)), they added TMCC compatibility to the engines. This effectively brought all the starter set type engines (if offered as LionChief Plus 2.0) into the Legacy control realm (see note above re: TMCC backward compatibility). So you no longer need to use a LionChief remote control separately as was required with original LionChief or LionChief Plus engines (the original Plus meant that the engine would operate in conventional with no remote - and LionChief Plus 2.0 will still do that, just with the addition of being TMCC compatible)
3) See above description. With Lionchief Plus 2.0, there is no reason to discount these little engines, since thy can be run in TMCC mode(no LionChief remote required), and therefore controllable with Legacy.
4) Only if you are talking about varying the voltage to the track and controlling the MTH Protosound 2.0/3.0 engine in conventional mode. You can't acces any DCS features with Legacy.
-Dave