Cool, cool! '34 Chev body channeled on a Ford frame, means you'll have lots of options. Looks like a '32 Ford grille too?

Ultimately it's going to depend on what you want from the car. If you go the hardcore rat rod look you could leave that quarter patch as is, drive it in primer and enjoy. Neither the BBC or the blown SBC would be quite "accurate" for the hardcore, shifter types. Either you'd have to go for an sbc dressed up '50's style, an Olds, Caddy, or Hemi, or a cool lookin' Chev six!!

If you intend to keep the car for a "long" time (whatever that means) then you may want to think differently. Can't tell for sure, but it looks like you still have only the wood bracing inside. If you were going to unload the car in a few years or less, and the wood is still holding the body together well, that would be fine. For the longer term replacing it with steel tubing would be better for maintaining integrity of the body and the body work you might be doing. Someday this "rat rod" craze will fade. At that point, if you keep the car, you may want to build it to a higher standard. That quarter panel patch is going to take a lot of work to get smooth, especially around the belt line reveal. If you've got the skill and the time it could be a satisfying project to repair that and anything else similar on the body. If you have to hire it out it's going to run your cost up a bunch. Again, if you "love" the car, go for it. If it's just something passing through your life, it may not be worth the expense.