There are a lot of people that have done it, all are happy with it.
The only ones that ever had a problem were early, early on when there was an issue with pressing sleeves.
I think there's one member that has stroked his bike but I don't know who it is.
Known beneficial add ons to the big bore (excluding the expected intake and pipes): Carbs, Headwork, Cams, Ignitor remap.
Best sites for info/pricing it out...
Do it yourself kits cheap :
Fasteddysports.com Newbonneville.com Bellacorse.comKits where the sleeving is done so its a drop in kit:
Triumphperformanceusa.com Bonnevilleperformance.com Theres another one in Florida a few members swear by. I don't have a name or link but someone will chime in.
Anything bigger than a 904 you will be cracking and machining the cases. If you have to crack the bottom end you might as well go as BIG as you can.
Have fun in your searching for info on this...theres a ton of stuff on here about it, you just need to search.