Well I looked though this thread and I have some good safe advise for you. For starters. The beams need more plating, the radius arms should have a gusset in between the tubes (especially if they are made from mild steel),the shock hoops need more bracing (coilovers require and engine cage with triangulation), and the coils should always have 1-2" max pre-load (if not you need to change the spring rate or check to see if they are mounted correctly) You have a good base and from what I can see its all fixable. As far as welding on a ranger frame goes. it doesn't mater how you weld on it. Its a C-channel frame and will crack regardless of what its made of. C-channel frames flex period! The only way to eliminate the problem is to box it in or/and cage the truck front to back with the proper design. Frame flex is what can cause the frame to crack. In this case the tube will eventually crack before the frame does. Adding some triangulation and more kicker tubes will allow it to last longer though.
thanks for the advise...i already have allot of that fixed. I have added alot more metal to the engine cage, I have a new set of coils with plenty of preload, and i am in the process of a new set of beams. once i finish the new beams (i am actually trying to save a bit for set of used threat beams i found on DR lol) I will most likey make new radius arms that are heimed..I build this truck w/o ever really seing another prerunner in person before, living so far north. Now that i know ALOT more and helping friends doing similar builds, doing alot of trial and error, the truck should take a turn for the better really soon.