I tried to be polite.
If you have to ask if your mig welder will do the job, then you do not have the knowledge or skill to do the job.
you do get the tab welded on properly and in the exact right place it will distort the fork tube.
Then when you are flying down the road with a passenger on, think about that welded on tab to your cast fork.
Will it hold at a XX mph panic stop?
Tig is the way to go for a job like that, it will still distort the fork tube. I was welding 1/4 " aluminum yesterday using a TA185. (185 amps ac) Its not big enough, so I have to use helium/argon mix to get a hotter arc. Like said above, the weld needs to be done before it turns into a big mess.
A spool gun on DC is the other possibility, but its such a short weld that the cold start will make it difficult.
The original is a one piece cast part for a reason. I am a welder and I bought the fork legs.
Some good news. Like I said in an earlier post, I converted my /6 to twin disc brakes.
3 years ago me an my adult daughter were going through the twisties in the swamps with my brother riding along
on his Valkrie. A deer ran out in front of us. I had enough front brake to squeal the front tire. Impressed me for the old /6. We missed the deer.
The conversion is worth it, I just would not do it with a welder.
Best of luck