depends on your skill level. and what year 6B you start with.
I used to work for a diesel performance shop and truck pulled for several years before all the high school kids with their mommy's money ruined it.
Anyway, that 5 grand stroker in a confined environment like a motorhome is not only going to run hot, but be very hard to cool. 2nd. you can get a late 90s, I'd go 99-00 non-HP Cummins for less than 1000, in running order. Those truck are rusting out badly and you can get the whole truck usually for not much more if you look hard enough. Then you have two options, you can stay with the electronic injection pump and run something along the lines of a TST PowerMax 3 or similar tuner. a a stock 99, with the TST tuner, we saw an increase of 167 hp and 350 ft lbs at the rear wheels. putting you around 400 hp and 750 ft lbs at the tires, reliably. and stayed under the exhaust temps that wreck havoc on pistons. Add 4-5 hundred for the tuner. As for the transmissions. my pulling truck was putting 1350 ft lbs to the rear tires, in 10 years of pulling, dyno runs, drag races, somehow I never blew the transmission. Granted it was a NV4500 5 speed manual with a Southbend dual disc clutch. And guess what, they did put that very manual into a few motor homes. even school buses.
your other option would be to swap to a mechanical P7100 injection pump, then you can simply turn the power up and down with a simple screw driver.
If you source your parts right, you could do it and make more power at a more usable RPM with better fuel economy for near the same or LESS than a big block stroker. For comparison, I'm gonna have about 6500 in my darts 440 drive train, I'll only be making my 500-550 and 550-600 ft lbs. at the flywheel. Just the heads alone for a stroker BB are gonna set you back 1000-1500, cam kit- 500, stroker crank, rods and pistons 2000-3000. intake 2-3 hundred.
RB stroker: 3700 engine alone
Trans upgrade to handle that power: 1000-2000 plus converter.
Total 5-6 grand for maybe 650 hp and 700 ft lbs flywheel
Cummins, 1000-1200 is the going rate for a good used running motor
Tuner: 4-5 hundred (mechanical injection pump if you went that route would be a 1000.
NV4500/NV5600: 1000-1500.
Aftermarket injectors: 500
HX40 turbo: 500
Clutch: 900
Total for cummins swap with transmission: 5500-6000 for 650 hp and 1350 ft lbs at the rear wheels (I essentially gave you my truck's combo, it was also my daily driver and was featured in 8 lug diesel magazine years ago). Add 1500ish if you went automatic trans. (could go with an Allison swap for less). Oh and I averaged 18.6 mpg city/highway combined. a motorhome would be less but more than a big block stroker for sure.
