Wow, that was more help than I expected!!!Here's all I can tell you about Honda's parts numbering system:
The first 5 numbers identify the part 61101 = stay - the next 3 numbers indicate the first model the part was used on HCO = TRX250X 87, 88, 91 & 92 - the last 3 digits indicate the manufacturer of the part, a color or a production change (length, width, height, gauge of material, type of material, diameter of holes, location of holes, etc)
Honda is very good at superseding numbers 61101-HC0-000 superseded to 61101-HC0-010 which superseded to 61101-HC0-020 and 020 was discontinued - 61101-HC0-670 is obviously the same part (stay) and is used on HC0 models, but the big change is that the 91 and 92 models have folding foot pegs whereas the 87 and 88 has rigid pegs.
Part ending in 670 (used on 91 through 2006 250X and 300EX) looks the same on the parts breakdown, but if it were a direct replacement, Honda would have superseded 020 to 670 - they didn't. If you have one that is broken, get it repaired - if you don't have one at all, it might be worth spending $17 to get the 670 and find out how close it is to fitting. All the other stay parts are the same except key # 32 (an 8mm flat washer: 1987 used 94101-08800 - 91 and up used 94101-08000) If it's too long between the holes, a machine shop could shorten it or if the holes are different diameters, but line up you might just have to do some shimming. Perhaps there was a change in angles - a little re-bending might be all that's needed to make it fit.
If you decide to buy the 670 part and find out how different it is, let us know - others might benefit from the knowledge. If someone on here has already found out - chime in and let us know what you discovered.
Sorry I can't be of more help.