I think my 500 was 71 X 63, have you made an error with the 71.5 mm stroke (61.5) ? My Triumph was extremely quick however extremely difficult to ride well - almost impossible with 4 inch megaphones. I used a two into one pipe to make it ridable, however it was s till nasty. It definitely needed a 6 speed box, I only had the 4 speed CR box. In a way I liked it, it was a thrill a minute and almost indestructible.
Compared with that my Seeley 850 is chalk and cheese. The Seeley is lovely to ride, I can do almost anything with it. I've never ridden any other bike with so much torque. Even my mate's old 650 Triumph which was totally set up to pull hard and is a really good fast old jigger, did not have as much when I rode it years ago. I'm amazed that the 850 motor is so good with almost nothing done to it - I never believed in it so the bike stayed unraced for twenty years. I've got it to the stage where I can almost race it again - I have to find some cash before I am too old to do it justice. Might get there next May if I'm careful or lucky.
