It's amazing how many folks have opinions without actual experience. I put a 302 Ford in my 1934 pickup. I did NOT cut the firewall. I even used the mechanical fan. The secret was a Snow-White (Fresno CA) Opel water pump kit to replace the stock Ford water pump. I added a C4 auto trans so the saddle in the frame was modified. I had air conditioning. The problem with 34 Ford commercial vehicles is the sloping grille shell and the condenser for the AC was a very tight (poor) fit. As a "pure" Ford man ( originally I had a 307 Chevy and a 39 Ford trans) I wanted the truck to be ALL Ford. It is now because I replaced the 302 with a built flathead.
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Maybe you missed the point in a lot of the post. Don't believe you could pull your 302 installation and install a flathead to get it back to stock. No one is implying you can't install a Ford small block in any early Ford. I have done in many times as have thousands of others. The suggestions were for an installation that required virtually no modifications to the original vehicle which could not easily be undone.
Nice install by the way!
A man after my heart. When I've done one of these 'half-breeds', I've always lived by the philosophy of putting it in, with NO modifications that can't be removed easily, leaving NO evidence. NO cutting, NO welding, NO hole-drilling. So, the original engine can go back in, and no butchery will remain.
Just opinion, my way of doing it.
flathead fever makes a good point... there is a run in my area that has this rule. Although, the rule gets 'bent' a little, if you have a hood covering up the engine, sometimes, they will let the rule slide. (especially if you are buddies with the organizers.)