title pretty much sums up the question. found an old TRS boat with a bad merctrans. maybe i should just do the bravo thing, but i am kind of a sucker for bolt-in type work. danny glover's line from the lethal weapon series comes to mind...

Edited, I had the wrong info, check out the post below. By the way I had my 71c's built by Huber and they held 700 HP Naturally Aspirated on My Mistress with TRS and KONRAD Drives. No Problems. Always clear pink ATF

72C is 1" longer then the 71C, I would not expect 800 hp from a 71C, not enough room to add that many clutches...approx. 68ft lbs per clutch

looking for enough to handle warmed over 330. might look into alum heads, mainly to get a couple hunderd lbs outta the back. did some homework after posting. so, the engine doesn't have to go forward 5 inches for 72c?

Merc trans is 9" shorter than a B-W so yes you definitely have to move the engine forward. You also have to change the input shaft on the TRS outdrive. If you don't plan to go crazy on the power upgrade you could just stick with the merctrans. Here is some info on them from a guy that builds them.
http://www.kcmarinetr.com/MercTrans-Facts.aspx

This info is 100% correct. If you do decide to go with a BW trans the engine needs to be moved forward quite a bit (approx 10") The BW TRS tailstock is quote long on its own as the MercTrans is very short and the trans housing plugs right into the transom assy.(no separate tailstock) For the power level you will be running, KC Marine can upgrade the MercTrans to handle it reliably.

If you do decide to go with a BW-Velvet Drive but don't have the needed room in front of the engine, Konrad makes a custom tailstock that is about 3" shorter than the TRS but you will need to add a rear mount. (no mounting ears)

this is not an exotic application. i am trying to turn an old 24-7 into a driver-as opposed to a yard ornament. wifey gets uncomfortable at 50. i could live with a 4-cyl bayliner, but i don't wanna...my biggest fear was merctrans was impossible to get parts for. looks like that is not the case. looks like i am repairing what i have...well, don't have it yet. thanks everybody. much information...and much needed...