Yes, they require the conversion.
I have about $2000 wrapped up in mine. It's on it's 4th engine, two of which were 21's. About 6 sets of cvd's (rd logics are the best i've found for the price), 8 gallons of fuel, 4 sets of tires (couldn't make up my mind), 9 fuel tanks (one $50 aluminum one), lots of aluminum, misc roll bars....
nickle and dime my ass! Honestly though, that is how it came to be what it is. Started as a $399 maxx at the LHS. Didn't like the engine, tried a different .15, decided a .15 isn't enough for the truck, upgraded to a 21... the rest is history.