390 Auto Engagement gear and shaft repair?

Greetings all,
I'm new to this forum and have a WXC 610 and a 390 auto, along with a bunch of other makes. Question I have is:
I just got my 390 running. It's been in a barn since '86 Initially, it went into gear just fine. After a few rides around the yard, it stopped engaging and started chattering. Pulled the 1st gear clutch and then the main shaft out to find an older weld job done to both the dogs on the shaft and the dogs inside the drive gear. All four edges are now rounded off .
Searched buy part number to find none.
I did find a shaft from a 420, will it work? It does have a different part #
I did not find any drive gears anywhere. I am going to post pics here if I can.
Thanks

Dave pratt at tritrophy on eBay is a good supplier of nos or used parts.

George at Uptight offers a repair service for that. The 420 shaft will only fit the 420, it has a completely different gear engagement system.

Forrest Stahl repairs the shaft and gear. He's in Indiana Google his name and you'll find him. He's done a bunch of them for my friends.

Thanks for the info and hook ups. I will get with Forrest i think, and I did find tritrophy.
Thanks

Greetings all,
Just to close out this thread and for reference purposes, I have a pic of the repair of both shaft and gear. Found a local machinist who did it for me. Not cheap though. Tried calling the others but I think they are not easy to get a hold of.
Anyway, rode it today. All four gears