I don't see that as a major project in that U have the old one for spacing of the flanges.
In fact I have seen factory flange stock and from there once fastened to a flat surface welding up tubing to fabricate a manifold should not be all that complicated.
Being a low performing engine (not a 'tuned' racing car) it should a be relatively simple project.
LOL, 3 flanges + 3 elbows pointed vertically and you'd have a 'hotrod' tractor, mind U a bit noisy..
Were U nearby I'd even offer to make U one mainly for the challenge.
Bet U had fun removing those studs.