I have a stage-II Proton expansion chamber for Yamaha RX135 (for the 4-speed iirc) that was made to order with extra inclination to suit RX-Z too.
The end-can (Silencer) was also made a bit bigger and longer for some extra silencing but was given away long back to a friend whose same was stolen.
It has been re-plated once and the mount was reinforced as it was not totally stiff earlier.
The main-stand stop needs to be reinforced as constant impact hammers it upwards and has cracked a bit as the metal used this time around was not upto the mark.
I hope to get it done soon after mounting it on a RX-100 and taking measurements.
Pipe is useable without it but not street-legal or even neighbour friendly- you may have flower pots approaching you with great velocity if you start your bike in the compound.
Making an end-can similar to Proton's is not very difficult too.