I would buy a nice frame from the states. They aren't very expensive. Then have it acid dipped and galvanized. Then when its all prepped swap everything over. Otherwise you will just be fighting this many times over for a long time. Just do it right once and be done-its cheaper and less time consuming when all is over.
it's a bit early days to tell just from this picture. How is the rest of the chassis? How bad is the damage to opposing side c-section?
I think I would first take a BFG and start hitting the chassis to see just how much is there...
If the damage in the picture is all the rot there is, I think i would
1. Jig up the frame
2. Remove the rivits from the rusted out part
3. Have it duplicated (or duplicate it yourself. I found 4 mm steel is fairly easy to weld yourself. You can check my build thread)
4. Then reinstall
I would find another frame, jig/support your frame, cut the rusted section out with a band saw, cut the new section out of the new frame, weld in the new section with a MIG welder, grind the welds, prime and paint.
Will you be removing or lifting the body off first?
I live in NB Canada, this is normal. I'd probably get some 3/16" plate bent into an L shape. Cut out the rust to sound material and replace with the new metal. add doubler diamond plates on each end for added strength. That is how I did mine. You could try cutting up a 3/16 HSS tube but it springs badly when opened up.
looks fixable to me, i.e. enough frame meat all around the bad areas to weld to ... looks like an area where the water/road muck just sits ... I like the idea of L plating it, but I might plate the other side even though its overkill ... might want to consider drilling a hole in the bottom of the frame plate to let the water drain ... it isn't just a 4 series issue ... Jeep TJ's frames rot in the flat area just in front of the rear wheel probably for the same reason i.e. the water/muck sits there ...
It seems there are no easy answers and it comes down to a labour of love vs cost and time and how long do you plan on owning or getting $ for the truck once finished. As Chris Wilcox says go with 3/16th plate. that is the frame thickness not what the rust has reduced to, so one can see you lost 1/16th as you came up with 1/8th plate.
If you have any welding skill draw up what you need in steel and have a local steel shop bend up the channels make sure they fit together, a round hole that Toyota has designed and is in the inside frame was designed not to collapse on it self. When you look at the 70 series frames they are mostly c channel without holes, maybe toyota found out the frames filled with earth, mud and dirt ?
As for the wheel arches if the shop cannot bend them then you will have to cut and weld the sections your self and then fit the finished channels together. For welding do stitch welds, each weld being 1 inch to 2 inches long and space them out, if you do a continuous weld then you might as well have a box frame and end up with other issues if you do : warpage from heat bending, will not flex as well as original etc...
If you go this route then you must not leave it raw, my first choice is hot dip galvanizing and hitting it with some undercoat.
If you like the idea of the suspension kit you might factor that in while your at it or factor in a nice rear receiver hitch.
Also : check the other forums where others have used 60 and 80 series frames for their 45 rebuild.
Re : Kurt : ''one for sale in B.C. '' That may be the easiest, cheapest and less time !
Either way if you think you are having sleepless nights pondering the options that is just the beginning but in the end it is worth it.
I did a rebuild on my 45 and hot dipped it and it came out very well.
Yes ive takin in all you guys have said that for sure. I feel more confident about just fixing my current frame. I have a message into a shop 2hrs from me about the hot dip and galv. I do have a welding back ground and 2 in my shop. stick/tig, mig welder. Thanks for all the help and ideas guys!!!