Unsure of your exact car. Hpi has all shaft cars, the older belts you have to search through rs4 parts.
I did find this online.
https://www.rctech.net/forum/nitro-road/829027-original-hpi-nitro-rs4-manual.html
3 or 4 links to pdf or sites with manuals. 🖒
Nice ride. This car does have chassis parts on ebay. I've seen square older cooling heads, not the newer ones. The body mounts may be hard to find.
I can't find any gas tanks, if you do, make sure its a left. The shafts are right.