try a company called unitracts. they design retracting undercarriage units for a variaty of specific scale models and the quality of their product is second to non. they may not be the cheapest but at least you know your not going to get any hang ups meaning no belly landings. phew. They do mechanical and air units. try their site at
http://www.unitracts.co.uk/full_prices.html

also have a look out for the old Radio Control Scale Aircraft Quarterly Magazine. Over about 12? issues Rob Millinship didd a build on the kit and showed how to improve the kit. He modelled it as P7350 from the BBMF. She looked stunning. If you want copies personnal message me and will fish them out and do copies. will have to be snail mail as have no way of scanning.