theres cooler looking engine mounts, but these will do the job for just over 3 dollars!
if you dont want those mounts make sure you get a set that are the same hight, some are 15mm and are ment for non pullstart setups.
ok the specific os engine you want is the .18 CV-RX (code OSMG2104), this has a standard crank, rotary carb and recoil starter that will fit in your nitro 3.....
If you want to do it really cheap, go for the hpi black manifold upgrade for your nitro3 which i showed you in my last post and stick with the stock tuned pipe you got with the kit, get those no frills engine mounts and stick that cheap os motor in there. like in this pic.....
thats under 130 all in for some serious power!! add a 2 speed transmission and you have some serious top end to! (the 2 speeder will fit on the os motor no probs)