I was looking closer at the article earlier and even though it doesn't say, the picture of the motor looks like HPI stock motor which is a Saturn 27T mill and If it is then it's definitely a 540 size. Then a BL 36mm will def work and be the better route !

Jason,
I've completely rebuilt your SC18 with a BL combo and repaired the radio,if your curious send email addy via PM and I'll send you some pics.

there is a guy running a cc4600 with his geared for about 35mph on 2s at the LHS and the motor gets a little too hot (100f ambient doesn't help) so i think anything less than a 540 motor would just not cut it.

Well HPI shows the HPI version/Sidewinder ESC/Motor combo as a Option

Id like to know if the body could be modded to fit over a crt .5 =P

no the crt.5 is to wide and short