Hey, Kev -
Mine is a crate engine from GM - a 3.4 V6 as found in early 90's Camaros and Firebirds. Also S-series pickups and Jeep Cherokees, in an earlier version. The transmission is a T-5 from the same era.
Very little cutting involved, but there are a couple areas that need attention - both at the firewall. One is next to the steering column surround, and the other is under the area where the heater sits. Both are minor, but you do have to make allowances there. The radiator has to be moved forward, so the horizontal panel in front of the stock radiator has to be trimmed - not terribly difficult. All definitely do-able by those of us with average skills.
There have been some very interesting transplants done; some more modern, and lots of V8's. But the V8's require more fiddling, especially the fenderwells. Unless you're interested in a fire-breather, in my opinion V8's are nice, of course, but they're overkill. The V6 I'm putting in will double the original B's power, and weighs about the same, coupled with the 5-speed. Also, the way it's mounted, all of it sits behind the front crossmember, so weight distribution is very good.
Happy to share whatever info/experience I've garnered (and it's a LOT more than I thought it would be!); drop me a PM with your email address, and we can chat.
Mickey