The tool you use to mount the drill chuck looks like a universal Z collet holder. If so, ZZ collects can be found in almost any size you want. My Tree 2UVR uses those collects in a quick change system. Good stuff. I had a holder similar to yours in my old Gorton O-16a.

Chances are good that you've got a 30 B&S spindle. Those used to be fairly common on mid size mills back in the day.

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We are brothers and sisters doing time on the planet for better or worse. I'll take the better, if you don't mind.
- Stu Harmon