Quick and simple line boring bar

[Toolmaker51]

I'd hesitate to mill T-slots in carriage wings. While factory versions are seen, I'm betting there is extra width and thickness to support material removal...Now drilled/tapped/tapered pull dowels in a fixture plate I'd go for. T-slots, matrix of tapped holes and a few reamed for straight edges. Compound removed, covering cross slide. Some might cut away around the wings, weld plate above and across the notches to keep it off the ways.
I'd think a mag base drill beats pulling and setting up to mill the carriage by miles.
And your 100 year old LeBlond still produces! That is why we admire old iron. My Pratt & Whitney Jig Bore is 100 next week. Date on motor tag, I believe is 4 July 1917. Yes, more pictures to post, I know, I know.