Here's my approach to the drawbar problem. The spring applies 625 lbs working pressure at 5/8" compression. The stop bolt is adjusted to give full release at the quill's hard stop and will eventually be replaced with a motor driven stop that retracts except for tool changes. So far it works great manually. Takes pretty good pressure on the lever but not excessive.
Threads are 3/8" x 32 tpi on both ends of the OEM drawbar which is necked down to about 3/16 for most of its length. A 1/2" diameter extension was simple to make. McMasterCarr has taps. Used green loctite.
Threads are 3/4" x 32 tpi on the shaft. I cut those on the lathe as the tap costs about fifty bucks. No loctite needed.
The housing was a chunk of cast iron sewer pipe.
JB