Got my new intake
Bolting it up to a head isn't a bad idea. Remember, metal expands when heated. Clamping the runners to a table does nothing to confine the manifold up where the welding and heat exchange are happening. I would hate for you to spend your $30 for the welding, only to find out later that the mounting holes don't line up on your head because of a little twisting or creeping of the metal. Probably the final thing you will want to do is have an automotive machine shop hit it with a little resurfacing to true up the face of the runners.
My two cents,
Jerry