A couple of years ago I had a Bosscat that I ran around first with a 19T brushed setup, then with a Mamba Max 5700 setup on 6-cell NiMh. I did not race, but ran over gravel, dirt, grass, and other fun surfaces - the transmission never had an issue. Your results will vary of course, but I'm pretty confident that running a reasonable BL setup (think 2s, nothing manical like 7000 kV) will be ok - at least, things won't explode quickly.
I did end up selling it though, as a couple of crashes resulted in broken parts, and those parts were very frustrating to find, and took forever to get to the US.
I wish you luck! It's a fantastic buggy.
FYI, that site Anthoop linked to is where I used to find a couple of solid sellers of vintage Schumacher stuff - one guy in particular sold some outstanding items.