badmother

It all depends on the use, where you ride, how you ride..

Utility often means you want to carry more than on a "normal" bike. Stronger wheels on a MTB, also stronger frame. If you want to carry real heavy you want fat tyres, and that is easyer on a MTB.

Also gearing is often better suited. Often better brakes than road bikes. Lower center of gravity, and MTB`s is easy to get, also good second hand ones.

If you got rid of the fork on your MTB and got a extra long rigid fork, maybe it could be a start? Sometimes both wheels, tyres, steel rack, steelcranks and steel bars is making the bike heavy. If you can swap it for free or cheap maybe your frame can be used. All depends of your area. Here there is a lot of free stuff in the dumpsters.

Bars you can decide if you use canti brakes. My impression is that most longtails has got swept back bars, but maybe that is just what I want to see..