Looks like an ordinary threaded barrel insert and being staked by the dowel supports that.
Is there anything not obvious or can ya extract then drill and tap for an oversize insert per typical practice?
Having never done it before, that's exactly what I'd do. Timesert "Big Sert".
-JW
I think it's more than a Timesert.
Its very thick and has strangely coarse threads on the OD as I recall.
I've only dealt with one. I pulled the transmission (after draining it). Took it to the local welding artists Morehouse Welding. They tigged a stud into the original insert. This was an older Pan Head transmission, so it really needed that fifth mount for support due to the tin primaries. As far as I knew it held forever.
You are probably dealing with a Keensert.
http://www.repairengineering.com/keensert.html
And here's a chart that has the removal drill sizes.
https://www.arconic.com/fastening_systems/commercial/catalog/Catalogs/AFS5949%20Keysert_Keensert_Catalog%203-28-17.pdf