IMHO I see no problem with it. You aren't going to be overwhelmed with power, but on the other hand, you won't be overwhelmed with braking or cornering.

The only disadvantage I see is the reliability of an old Triumph. I love those bikes, my dad used to build them back in the day, but they're not like a Japanese bike where it never leaks and always fires up. As long as you don't mind turning a wrench here and there, go for it.