FirstGenLegacy

Hi! I'm generally new to RC, and recently bought a nitro rc car from CEN. it's the 1:16 scale MG16 monster truck, when I got it it wasn't running. Fortunately I was able to get it running with a quick fine tune to the carb, and some tlc (tear down, rebuild).
Currently, only mods I've got are rebuilt shocks with RS4 shock oil, a Traxxas Stampede exhaust, a fuel filter for added security, beefier tires, re-directed the pull start, cleaned the air filter (and re-oiled). I've ran it with 20%, and 33% nitro fuel, seems that between the two it makes very minor differences (unlike real cars), and I recently fitted a .15 (2.5cc) Traxxas Rustler cylinder head (cooling head) onto it, because I got a relatively good deal on it.

My major questions are, if I wanted to swap motors, or do any other mods such as roll-cage, two speed, reverse.
What fits? what doesnt?

I've got a spare OS slide motor laying around, will that fit?

I just want to do as many mods as I can with this car for as cheap as I can, I would be asking on the CEN Racing forums, but they've been having issues with the website, and I cannot sign up. Hopes it's OK that I post here.

Thanks for viewing the thread!