Joe, after reading some of the responses here, It is best that you forget most of it and Go talk to a actual welder in your area....The person who told you It is not good to weld on frame steel is correct, But not in this case. A model A frame is not actual frame steel. Frame Steel is tempered and is only used on large trucks such as semi's and medium duty trucks. Also to the guy who said his boxing plates was only "stitch welded" but had gaps, By rights the plates should be welded all the way, but If you do not have a big HP motor, And drive it on good smooth pavment, Your prolly ok. It sounds like the guy who built it just got lazy, But with that said, what other areas did he fudge on?....It is stuff like this that scares me. We all want to have fun and we all love hot rods, But I can't tell you how many times I have seen this...."Goober" builds a car in his backyard using duck tape, bailing wire and about 50 tubes of "JB weld" Sells it to someone who doesn't know any better, And then if they are lucky they find the problems before someone gets hurt.
Why, oh why won't this myth die? Not only are nearly all automotive frames made of mild steel, but even medium duty trucks (up to 15,000 lbs GVW) use mild steel frames that are very weldable. GM's Upfitter site provides info for truck body builders who modify new trucks. One part of this site is a set of "best practices" manuals and one of those provides excellent detail on exactly how to lengthen or shorten their truck frames, including welding info. Read it, even if you are having someone else do the welding. At least then you'll know whether the person doing your welding really has a clue or not. http://www.gmupfitter.com/best_practice_manuals.html Click on the Chassis button.
We have cut tri axle dump trucks in half and welded them back togather with no problem. We carry 25-30 ton every day. Cut them on an angle put a inner liner inside and bolt it. It wont go anywhere.
He means to fish plate it, to weld a support plate on the backside that overlaps both sides of where you butt welded the frame pieces. Do this before you box the frame. Bolts are unnecessary and ugly for this application, but if you ever were to use bolts for something like that then yes grade 8.
A frame that should have been boxed. The break is so old, that it was probably done back when boxing the frame wasn't common.. Guessing, by the hacked recessed firewall job, that looks like it was done back in the 30's - 40's. Then again, the car was rolled, so that could have done it too.
If frame welding was not an acceptable practice then every drag strip would be littered with death and destruction, wouldn't it? Back 1/2 job-welded. Cages-welded to the frame. Rear axle housings-narrowed and welded. Full front strut suspension-welded. Get it? Most of those guys stress their cars harder than you ever may. Relax and have fun with your build. This disease attacks many home builders. "Joe Experienced-in-everything has to attempt to save your life or show you how to re-invent internal combustion. Logic and safety 1st trumps free advice every time.
Remember, there are two things in life where penetration is really important... one of them is welding.