To be honest, if the motorhome has the 454, I'd say unless engine has thrown a rod, rebuild what's there, if you can swing it, get the TBI installed. Raveson had a 345 and went to TBI conversion. Wasn't cheap, but he remarked to me that it was well worth the expense, since he went on a 4 month trip from Florida all the way out to West Coast, up to Oregon, and meandered his way back to Florida. Mind you, he towed a Jeep Wrangler the entire trip. He spoke of LOTS better acceleration, quite a bit more mph through the Rockies, and a bit better mpg as well. Mind you, I believe he did this all at about 70 mph.
TBI will be my next HUGE investment into my Airstream.
Good Luck, Derek