Wow, that was a long time ago!
I do use it regularly now. It took me forever to actually add in the pins that retain the camlocks, finally did a few months ago.
As for changes I would make? Nothing big.
I would maybe try and reduce the thickness a touch (maybe 1/4"), on the back side that mates to the table, but would need to check the length of the pins, there may be a reason I made it with that little bit extra material.
And maybe increase the diameter to 5.5 or 6" to fully capture the heads of the 4 hold down bolts (purely cosmetic)
I also made mine from mild steel (1018 I think) and its holding up ok without hardening.
I think the cams are hardened and they have enough funny geometry to make them a pain to make - i.e. at least 3 or 4 setups, so buying them from somewhere (i.e. Grizzly etc.) made sense to me.
The center through bore is 1.5" and could even be made a bit larger, but as you say I think the chuck is only 1.5" and my 6" table only has an MT2 center hole (much smaller).
One of the little time savers is that once the adapter is centered on the table, it stays that way and the chuck can just be mounted up straight from the lathe, with virtually no worry about it being off axis (at least for my tolerances
)
Its actually been such a convenience using the chuck on the mill I often just mount the 4th axis vertically so I can hold round items easily. To the point that I've been thinking about making a rectangular one to hold in my vise or flat on the table so I don't need to keep repositioning the 4th axis....
A few random pics of it attached here. The last 2 show the convenience of the adapter, the front crankcase was held in the 5C collet chuck on the lathe, and I needed to drill some holes so onto the 4th axis vertically (good thing I have lots of room), and then I was back to the lathe (not shown) and then back to the mill to make the radial holes for the lifters and pushrods, all without removing the item from the chuck and needing to recenter.
Mike