Did you check your rear mounts- if one is toast/loose/broken, it might cause the engine to lean during cornering. When I bought my '50 3600, the harmonic balancer was barely rubbing against the front mount cover. After pulling the engine I found a squishy front rubber block in there... sounds to me like one of your mounts is either loose or worn out. It is possible that even your rear crossmember could be cracked/loose.
Also, I'd like to be there to see someone try to "shake" a 700 lb engine to see if the mounts are bad....
I think the only way to check it out would be to try to gently jack each one of the rear mounts to see if the trans lifts at all... Good luck!
You can also put the parking brake on, put it in gear and gently let out the clutch while someone watches the engine to see if it moves/rolls left/right at all.
