Ill leave the topic on what engine to get alone because im sure someone will mention the engine you shoould look at (made os O.S.)
Anywho its not that hard to swtich from rotary to slide. just a new servo "horn" is it called? thats designed for slide carbs. If your looking at getting the TZ engine just do a bit more research on the engine to see if you really need the power ( power doesnt always = speed ) and the other main thing you might want to know about the engine (TZ) is the piston and sleeve is $80 motherfu***ng dollars!!![:@] Which really sucks when u can get a .18 cvr for 100 bucks.

My LHS is selling TZ engine for $135 so im looking at getting ...another one