Mesa board advice

I have a Cincinnati Arrow 1000 that I am starting a retrofit on. I am looking to be as little invasive as possible and utilize most of the wiring. The beauty of this mill was it had an acramatic control on it which was windows NT based and the control had pc type components on it. I have my motherboard installed as well as a 7i92h/7i77/7i73 combo. I want to get 2 7i69 boards for the inputs and outputs but I am a little confused on how to hook them up in conjunction with the 7i73. The inputs/outputs are coming from a opto22 rack and are idc50 pin connectors. Any help much appreciated.

I would suggest a 7I90HD rather than a 7I69 as they are cheaper and we have them in stock
The 7I90HD also will drive 3X 24 I/O Opto 22 type racks rather than the 7I69s 2X racks
You will also require a couple more sserial ports. These can come from a 7I74 or a 7I85

Thanks for the help. So if I get the 7i85 to interface with the 7i90hd I assume that the 7i85 would be driven off of the 2nd header on the 7i92h? I also have a spare 7i78 board, could I use it for the 2nd rs-422 port needed to drive the 7i90hd? This way i would have an rs422 on the 7i77 and a rs422 on the 7i78.

Yes, if you have a 7I78, you could drive both a 7I73 and a 7I90HD

So I have been doing a little investigating and it seems that the inputs and outputs on this are 24v. I think this rules out the 7i90hd? I was thinking that a 7i85 along with a 7i70 and 7i71 would give me all the IO that I would need if the 7i90hd is unsuitable. Does this seem like a sensible path? I suppose I could do some optocouplers to get the voltage down for the 7i90hd to handle it but that may be a crap ton of optos (48 x 2).

I thought you had OPTO22 racks for the actual I/O.
The 7I90HD will drive 3 x 24 I/O OPTO22 5V interface
racks (50 pin connector style)

I thought they were opto22s but I may be mistaken. They look like opto22s but are made by colter products out of England. Attached are some pics .