You may want to check with an trans expert like Tranny Tom to see what year cases were the strongest. K case:
Is your torque converter cover thin sheet metal or something heavy? Here are pictures of how GM mounted the 700r4s on the last of the straight axle trucks, is your cover similar?
Its hard to picture a slowly bleeding down jack gently loading the tranny case causing much of a problem, but who knows. Probably a good idea to run with the cover on though.