I am building new hives for my girls and plan on moving them in. Those of you that have experience with TBH's what would be your advice?

My old hives are about 24 inch long bars, the new ones are 18 with about 15-15 1/2 inches of space for comb. I figured I would move them in early spring before they built up much new comb - would this be best? What would be the best way to move them in? Just dump the bees in like a new swarm and remove the old hive? I could attach the smaller new bars to the longer bars and let them build comb on them then remove them and put them in the new hive. I'd really rather not mess with the folding type frames, detaching the present combs and moving them to the new hives that way.

Ok, I've rambled on enough now, what would the pro's do in this situation? Thanks for all the help!!!