How Do I Shorten an Antique Truck frame?

I have a 1941 WWII Dodge pickup truck. I found a perfect ambulance frame for it, identical but 7" longerin the center section. I have been told I can cut it at a 45 dgree angle and mig weld it back together. This would be done about center of theframe, between the axles. I want to keep it "original" so don't want to add gussets. It's built in two layers of steel, about 3/16" and 1/8". I don't think these old frames were hardened. Will this hold okay? Should I have a certified weldor do it?

Also, is there any way to replace the large factory rivets to replace cross a memeber? Again, I want to keep it as close to original as possible.

I would appreciate any expert advice,
Maurice

 

[11echo]

I won't use a MIG welder to do this job, too light a weld. This is a normal ARC welding operation, use 6013 or 6011 rod. Trick of it is, most of the welding is in a vertical position. You'll have to be the judge if your good enough welder to do this. Also I think I would use a fish plate to strengthen this weld up, especially with a vehicle of this weight. GOOD LUCK!