I've been reworking every issue (and there are many) as they come along. I just never checked this sleeve out with an indicator before. I only did this, as I put a 4MT test bar in this sleeve and found a killer amount of runout at the end of the bar. This traced it back to the sleeve not fitting the spindle. And I believe it to be the spindle that is the problem.
I did measure to the best of my metrology that the sleeve was 90mm at its major diameter, and had a 1:20 taper angle. The spindle I've not measured yet, as there is .2" in 4 inches, and I need to make a dial indicator holder, to hold the small 1" dial (.25 inch travel) indicator, that will fit inside the opening. I know I don't have to sweep all 4 inches to collect enough data on the taper.
This is now another project to make a holder for the indicator I have.
I don't believe the compound slide has enough travel to install the tool post grinder on and machine via this path, as this taper length is about 4.5 inches.
But I want to measure the sleeve more accurately first. I'm waiting on a bench center from eBay, that in conjunction with a sine plate I will determine the angle of this sleeve.
This sleeve is hardened, so it would have to be ground, if that is the path I go. But if it is the spindle opening, that is where I want this fixed, so I can say that it is a 90mm gauge metric taper of 1:20. Just in case I find tooling in the future, but I've not seen the DIN specs as they want money just to look at this.
Yes, the simple solution is to cut a new taper sleeve that fits the existing lathe as is. It's only job in life is to keep a center centered, and will not drive torque.