Frame steel question

I need to make a rear mono shock bracket and some other bracing on my 80 kz1000 .
I have some 1 1/4 solid steel car axles I could use or should I just order some 4130 chrome molly ?
I know it's definitely strong enough but worried about tig welding sold to tube steel.

No need for chrome moly.
Just use mild steel , original frame material isn't that great and nothing special.

Thanks , Do you know what the exact size is? Looks like 1 1/4 not sure about the wall thickness.

Wall thickness varies with tube diameter but the main loop and top tubes are 2.4mm thick and the smaller top subframe rails are 2.0 mm thick.