here's link
http://www.foxmanufacturing.com/index.php
i think Made In USA Guillows kits and Fox engines are a good combination!
the engine mount on Fox is different than Cox but i think it'll work.
they come in .15 that might be too much for kits that used to use Cox .010.
then they have a 25, 40 and 50.after that prices go into the stratosphere.
here's pic of 35 Stunt and description.
'In production since 1948, current motor is near replica of 1951 model. Only available in control line form. A million or modelers have learned to fly with this motor.'