Evan is giving you the correct method to follow. If you choose to ignore his advice and do things your way, whatever errors you build in will return to bite you where you sit after it's difficult, or maybe impossible to correct them. When I built and/or repaired round track race car frames, we not only supported the frame on screw-type stands in several places before doing any cutting or welding, we also used floor-mounted anchor chains to keep it that way.
Jerry
