I used a 3550 for 10,000 miles with no problem on a 400 hp BB.
Don't now where your at but Classic Transmission in Fort Worth is best price I found. You can pick up good used 3550s cheap. I have one in the shop I would sell for $500.
Don't know about fit. It fit my Lone Star Classics.
Your HP is gonna have a lot to do with gearing. 2.88 looks a little low to me unless you run LOTS of hp. I run 3.25 rear with 25.7 tires with well over 400 RWHP. Play with this calculator
http://www.secondstrike.com/technical/gearcalc.asp
This site also has a lot of good info.
http://www.5speedtransmissions.com/index.html
Hope this helps
Bruce