Glider pilots rule
Mark,
Your 50+ hours in gliders will I am sure make it very easy for you to handle the practical aspects of flying powered aircraft (specially if it was amassed from short flights in poor soaring conditions in the UK). I know that I had at least 100 take offs and landings in gliders by the 50 hour point when flying in the UK! Its landings that count in my book!
I would recommend you search out a power school that favours training in tail-draggers like a Citabria or Piper cub. Gliders are after all tailwheel aircraft. You will feel right at home and you will learn more than can be taught in a nose-dragger like a Cessna. After a few hours you will have worked which instructor you are comfotable and working well with. Remember you are the customer and it should be a very enjoyable experience. if its not find another school.
I dont know what the time requirements are now but I went PPL in the UK on the basis of a Silver C. When I came to Oz they wanted to give me a restricted PPL but I argued that I had cross-country glider time in the UK in my glider log book and manager to get granted the unrestricted PPL.
But really in the big scheme of things dont worry about completing it in record time. Choose your instructor well and if you have to do 40 odds hours use it to learn more advanced skills like instrument approaches etc. It wont be in the test ofcourse
OOW