Rear set "triangles" and strengthening the frame..

Hi all,

Just a quick thought, was looking the rear sets a friend has and how he buys aftermarket rear sets that just bolt onto the frame, which sort of wondered how'd you go around it for a Bantam. Bit of a Newbie question this, but just need assurance from "experts" lol..
Are these "triangles" just a simple bodge-up build with 3 pieces of ally or steel etc, or do they take time to develop?

Also I would just like to ask what are the best things to do to a frame with strengthening and all seeing I am 15 1/2 stone and 6' 7", but the weight is gaining due to sport. I know I'll have to move the seat back very far to allow me to "lie flat" as you say...

T