Wow... 4 gauge wires, three of 'em, and 30 feet long...... You're gonna need a chain fall to lift that thing up to hang it on the wall when you're done. After you figure out how to roll it up of course.
As far as amps, that's absolutely glorious overkill. No worries there.
I'm going with that welder uses a 6-50 plug/outlet? That's pretty common for welders (even ones that "should" have a smaller plug).... You're gonna have a heckuva time getting plugs and sockets that small, with terminals that are going to work reliably (safely) with that wire. Rolling it up and unrolling it is going to be a nightmare.
These are not a continuous load. That downsizes the wires tremendously, and the duty cycle downsizes it more. I'm pretty sure you could run that welder legit off of 10 gauge J cord. (Do your own math though.... It takes a lot of googling to piece together all the sections and all the tables you'll need, from a book that's not supposed to be on Google.... What you need is on the welder's data plate, and NEC 630.11
That of course is a minimum standard, I'd have no issues stepping up "a" size, but my gut hunch says that poor "cheated" connections are going to be a reliability/safety/fire issue. Not the wire, not the plug/receptacle ends, but the joining of the two.
As I said though, the wire it's self- That, in and of it's self is not an issue. That wire won't even know the difference when you turn the welder on. It's the rest of the project that bugs me. And that IS more than likely surmountable with enough time and effort, sleuthing out solutions for hooking up things in a way no electrician would ever do, so therefore the notion is not well supported with convenient products that work right out of the box.