i have the engine out of my 79 the lower control amr brackets at one time have been rewelded in dont know why.
now with a closer look the frame has small cracke next to where the welds are
if see pic's of other people welding webbins at the lower controle arm mounts and nthe engine mounts and the ft frame horns for the bumper support
my ? #1 is why do u think these had to be rewelded
and #2 is can all the webbing welds be done with the body on the frame
fyi i have a 383 crate engine going in spec. are 475hp 525 ft
700r4 behind it
3:73 cast iron rear end from duntov
and i seen pic's of some cars having a adjustable strut bar in the front
what came out of the car was a 350 hp th350 trans with a 2400 stall and the o.e. rear end with 3:73 gears

 

Maybe yours was damaged from an accident and rewelded.
As long as the area is clear for welding, you should be able to repair it.
It wouldn't hurt to add a spreader bar up front.

http://www.vbandp.com/C2-C3-Corvette...r-Bar-Kit.html

I beefed mine up by adding gussets.

 

where do u find an adjustable spreader bar kit r u adding to your frame
and i was going to use the old cross member for the metal needed on reinforcing the lower control arm brackets

 

Here's a pic of Vette Brake Products spreader bar. They have 2 types depending if you have electric fans or not. Also, here's the link to their site again. I have the welded type.

http://www.vbandp.com/C2-C3-Corvette...r-Bar-Kit.html