I have stuck the Caster brushless RTR kit in the car to test if it can handle it, as well as finally got all the bits to start soldering connectors. (Hobbywing 13.5T motor [I think] 35A ESC). It really accelerates!
Think I may have a problem however, the hubs on these things are not particularly good and can give a fair amount of wobble. Combined with no spare parts, solid plastic bumper (ouch), no adjustment to camber and shocks that aren't oil filled - I suspect this is going to prove to be a futile exercise and would be better with just a simple chassis like Ansmann ARE-2 (£30 new on ebay) to keep costs down.
You'll notice I removed the platform on the right side of the car (under the old ESC) to support the use of Saddle Lipos.
The car needs a good clean, the chassis is caked in 10+ years of dust