Sounds like a good deal to me as long as it runs well!
That is pretty decent mileage. The key thing I always hear to look for in the V6 SHOs is to make sure the 60k mileage maintenance was done as well as the 120k maintenance (same as 60k IIRC, but since it's right there, you could have it done if it wasn't already). I was actually sort of planning to get a gen 2 SHO sometime this summer maybe, so I'd be in the same boat as you as far as having a SHO play car and SLO daily driver.
Sorry, got sidetracked - I don't know a whole lot about SHO trannys - but AFAIK the manuals will last quite a while as long as they are treated well and have fluids changed regularly - it's all about maintenance with our cars, of course, I'm sure you know that.
Good luck!