thats a pretty clean lookin maxx ya found there bud! nice find
looks like a standard 2.5, although the 2.5 is pretty quick to begin with. i have a 2.5r, which is basically the same thing with a machined blue head and slightly more aggressive porting. id probably leave it on there til it blows, give ya some time to get used to the way the maxx handles before throwing a speed monster engine in there. also traxxas has a trade up program if ya didnt know you can get a 3.3 if you trade your blown 2.5 for like 80 bucks i believe it is. one tip to get a lil more low end out of the 2.5, get yourself a THS racing exhaust system for it. costs bout 50 bucks for the header and pipe and will give you ALOT more power than that plastic pipe will. super loud too lol. if that truck is a first gen 2.5 maxx it still has reverse and retains all the driveline parts from the original maxx, and a 3.3 will just eat those parts alive without mercy lol