That's why the old auto mags were great. they told you how to do thing like this, untoll the advertizers shut them down. "Street Rodder" was the best. I think they started the street rod industry.
I did a 39 car with a Heights MII had a pan maybe a truck with large cleanout hole.
If you keep part of cross member you can bolt like a stock setup.
Once you do that you can go any engine you want.
Flathead with c4 works good.
I wanted a "chassis engineering" rear leaf spring kit for my 36 coupe, there gone now! sad.