I think ( From memory ) that Cooper ( And others ) racing cars wanted to use Manx Norton engines in their cars, but Norton would only sell complete bikes, so that left spare rolling chassis. At the time the Norton featherbed frame and roadholder forks were the best available and people fitted Triumph pre unit T110 or T120 engines into them as these were some of the best engines of the day. That was back in the fifties and sixties.
All tritons are home made and as such quality and price vary greatly. If you are thinking of buying one the old adage of '' Take someone with you who knows what they are looking at'' is a definite requirement.
I had a triton with weslake 8 valve heads fitted and an 8 leading shoe front brake ( A nightmare to set up )and out of about 30 bikes I've owned this is the one I wish I'd kept. I sold it to buy a Ducati 860GTS. There you go
Hope that helps.. And welcome to the board
Phil