lux turn cnc retrofit spindle upgrade

first time posting:)
                          I've recently got myself and old lux turn cnc lathe and am in the process of a retrofit with linux cnc.  Im looking at using one of the mesa cards probably the 7i76e and I am trying to get some advice on which motor driver for the spindle to upgrade to.  The old spindle was a 450w dc motor but the driver board is missing and while the machine has the pully for a spindle encoder including a dangling timing belt this is a missing element.
so I am thinking of a more modern way to be able to achieve threading and constant surface speed cutting.

I've looked at one 1.2kw ac servo drive that apparently is using modbus over rs-232 /rs-485 and I am wondering how I am going to be able to achieve the control I would need with the 7i76e.

Has anyone such experience with such a servo drive for the spindle and the efforts Im going to have to go through to get this working?  Ive seen other ac servo motors on aliexpress that use a 0-10v input but these dont get stocked in the EU presently and Id like to avoid long waiting times.

As for the rest of the machine its using 2 steppers for the main axis and another stepper for an 8 turret tool changer.




 

Finding a pwm servo driver at 90v is slim pickings in ebay unless I get it from the us..then the price is mostly the same and I'm stiuck with a system that's not easy to repair down the road. The encoder though would be easy. I can also buy a DC motor driver like inise on the milling machine"optimum bf20" but then I'm going to also need a breakout for isolation for the 0-10 v and I'm not sure how to deal with direction without a little hacking.  The AC induction motor is possible but the form factor at the power requirements mean housing it externally and then adding a brake is also more challenging.

Good question on the pwm input. I've just got the manual sent to me somill go through it now and have a look. I suspect that implementing both modes of operation could be good..I think others have done the same in the past but I'm not able to find the info of driving both step/dir and pwm yet.

attached is the pdf manual for the drive, I am yet to really go though it but I think posting it can serve to help others who are looking for it.A1- SVD15 manual in PDF formatits split into 2 parts because of the file size

On page 20
10V~+10V 。 Analog voltage input port.
Speed or torque control used to receive
speed or torque instructions. Voltage input
range -10V~+10V.
Not sure how I'm going to generate that +-10v as I'm guessing the standard has been the 0-10v

had more time to look through the manual,  looks like either it can use an analog input or step/dir. 
Now to pair it with a bunch of hardware
any decent alternatives to the 7i76E for high speed encoder feedback? - by alternatives I mean ones that are available:)

I've not set up an electronic  enclosure before and I am sure there is a ton for things that this is going to need apart rom the stepper drivers I have

Probably more isolation or noise filtering for a servo motor like this Imagine.
 

@andypugh thanks for helping me sort through this,
                                                                                   Reverse direction would be great for ridgid tapping:) I have only seen C89 on the  cncforpc store but I would love to know alternatives as it may be easier for me to source in Germany.  I can also build one if I knew of any schematics DIY options(i have an electronics lab here).

Yes the drive has step and direction input modes  I can also interrace with the encoder but it is 2500ppr/10000per turn so thats way too much I am guessing if I dont have a 7i76E.  

Only problem now is interfacing it with a cnc controller that I can actually get my hands on or perhaps figure this out with a less high resolution encoder on the spindle for feedback for now with a break out board of some kind.  If I can figure out the last part I can more or less start to build everything.

cheers