If your gonna do a self build on a rotary there is a yank company called Rotary aviation that will supply full rebuild kits for the 13B engine at very good prices.......they also sell videos of the rebuild being carried out by a bloke called Bruce Turrentine (sp) which is supposed to be a must buy for the DIY'er..........

Also, when i had mine, i sent it up to Pip @WGT in cheshire, and the man is mint! Top bloke, nice as pie and will tell you straight.