Yep, do a search. I have this problem as well. From what I understand, you already answered your question. Replacing the FRAME mounts to 350 mounts is your best bet. Especially since you already have the motor out. That way you won't have to worry about any problems. When I put my 350 engine in my 307 car, it broke the driver's side mount. My uncle fabbed a torque strap connected from the engine to the frame, so it keeps it under control for now, but when the time comes, I will be replacing the FRAME and ENGINE mounts.