For my money, mount the lathe on a firm (NOT flexible) steel bench, made out of angle iron or box section.
having done that, level the lathe so that there is no twist in the bed from headstock to tailstock
The ML7 bed is relatively flexible. Once you have it twist free, with sensible torque on the fixings, do not put any additional "nip" on any of the fixings "for good measure" or you put twist back into it.
If twisted, you will never turn taper free. The Myford instruction book tells how to machine test pieces to check, and where to shim / adjust if twisted. My preference is to use as sensitive a spirit leveas possible and check at each end, and adjust until both ends read the same. This will mean a lot of iterative adjustments, but the time spent is worthwhile in terms of accuracy in the long term.
Just be patient and keep at it!
Good Luck
Howard