The 35-40 Ford frames are pretty substantial, I've built coupes, sedans & a 39 convertible, the only boxing I did was in the front of the frame from the crossmember to the firewall. HRP
If I were to box my 35 or 36 Ford Pickups, I would go this route. https://www.wolfesmetalfabrication.com/3540fordboxingplates.html
I did several 35-40 customer straight axle chassis using original frames and never boxed anything. My 40 standard is this way and is fine. Only time I boxed the front was when installing a Heidt's Super Ride II and I used the boxing plates they provided. Never boxed the rear on original chassis as I always used the CE parallel rear spring kit. I also did quite a few using fully boxed repro rails.
My avatar car was boxed front to rear going slowly here and there, back and forth, side to side. No warping or any problems. I did the full rail box because it has a blown hemi in it. Most can just do the engine area and be fine
These are stout frames right off the factory floor. Maybe if one was running big HP and TQs? Mine is boxed around the Hemi but nothing from the firewall back. Of course, it is a PU and is never going to hook up anyway.
I wouldn't bet on that. I did the same system for a friend running a Blown Big Block GM and Slicks. His works just fine. Runs low 10's. Any faster and he would need a cage. He doesn't want to go there.
My old '46 Ford club coupe ran Joe Reath's 1958 hemi (out of his rail) with a Hansen 671 pump on the street and never a problem. (I suspected a 'twist had to have happened, so hung trammels under, nary a twist. My 'new' '47 Ford Fordor will get a nice 390 FE, RAT Ford synchro 3 peed (on the column: Like all the Fordors! I don't anticipate any additions or boxing here, either. These are strong chassised cars, (say "chassied") Even the factory steering is preferable. (Gemmer box, good linkage design) Consequently, it will be worth the surgery on the oil pan to move the sump rearward. But frame boxing? Not on this C-dan...
I have a set of boxing plates for my 36 build, but it's because I wanna drill and tap them for all my lines so that it is all nice and neat. Other than that, it's just for aesthetics.
I know it's not necessary to box the chassis on these cars (our '36 sedan wasn't boxed and we rolled many miles on that car), however I chose to box the chassis on our '38 cabriolet because it doesn't have the benefit of the roof to help stiffen the car. I made simple 1/8" plates, drilled and cut plenty of access holes and mounted them so I had a nice corner weld that could be ground smooth when done. Here are some photos showing tacking in the plates with the crossmember removed and then the chassis after the crossmember was re-installed (from my build thread).
Seem to recall at least one of the parallel spring kits provided additional support in the areas most prone to rust.
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