Not the first owner and it's 11+ years old. Think I'm stuck with it.
Hold that thought I may take you up on it. 7005 can be heat treated to improve it's strength again after welding or so I have read on the internet so it must be true. Also I don't think a catastrophic failure will occur from a loose head set. More like I will notice it pull over see the problem and ride home slowly. Seldom ride over 20-25MPH anyway probly one ride to get max speed and take my rightful place in the ebike insanity club will be about enough. I think that a support ring in addition to welding would be in my best interest. What are your thoughts on that?
I still wouldn't weld on it. Heat treating aluminum properly involves a solution heat treat and artificial aging. Two separate processes that consume a LOT of energy. Usually it's between $600-900 just to get that done, unless you can get it in with someone else's stuff, find a shop with small facilities, or get a buddy deal, and even then, you still have to worry about warping.
Even though you won't be going fast, you are going to be adding weight. The lightest I could get a 3220 powered rig with 15ah of lipo is 75 lbs which adds significant stress to the frame. Also, where that crack is, if you do hit a deep pothole, curb, try to bunny hop or jump it, even at 25mph, the stress will focus on that area and you could have catastrophic failure. Look for the video of the guy riding down the volcano to see what it looks like when your fork comes off.
Thin aluminum generally doesn't bend a little when it's already cracked and stressed way beyond it's limits. It just breaks.
Bikes are designed using the thinnest materials that will do the job for an average rider, at average weight, and average speeds. You'll be exceeding all of those parameters just by the nature of what you're building so take it seriously.
I'm trying to sell my shop and tools as hard as I can so this is a limited time free offer. Just get me a couple of measurements and your address and I'll mail you your best solution with installation instructions by the end of the week.