I’m doing some pondering...I’ve got a 1986 mercruiser 330 with borg Warner transmission and TRS drive, I’m thinking of swapping in a pair of aluminum small blocks with alpha drives...

is there a site or table that lists weights? Or does anyone have an idea?

Go with Bravo drives if you do the swap. Alphas will only handle 300hp and not as much torque.
Probably will be about 300-400lbs a side lighter