Welds are never as strong as base metal and typically weaken the piece just beside the weld itself. I have not viewed your links but without looking I bet the failure was near the weld bead but not the bead itself. This area called the HAZ heat affected zone. Is why TIG is Strongest weld has smallest HAZ.

Having failed once another reweld of the same type in the same place will likely fail again. I would recommend something different this time, either bolting or adding gussets or other material to support the weld.

Dennis is correct on using shoulder bolts so threads do not wallow the holes. McMaster Carr or Aircraft Spruce will most likley have the right size. Fastenal has less selection...in my opinion.

R-Bo

1959 Apache 1/2 ton Big Window, Short bed Fleetside (under reconstruction)
1966 GMC 305V6 in the family