Don't know how accurate you want it, but the M-3 TD had a very unique 75mm gun, which was totally different from the PAK 40.

It was an obsolete AA gun with the old WW I round, manual breech ring and outrageously heavy for that half track. Many of them turned over on a 45% slope and handling of the half track was difficult. El Mod looks like the way to go and pics or videos would be great.