Top choices
You say it does NOT need to be a certified engine. Than engines made from either ECI and Superior will do. Parts are comprable. Some feel the ECI cylinder is better (for corrosion resistance). Some feel the Superior induction (oil pan) is better, at least that is what their ad says. Call Mattituck.
I built my own Lyc from spare parts, but consistently hear great things about the following.
Mattituck, NY:
http://www.mattituck.com/
Aerosport, BC Canada:
http://www.aerosportpower.com/
For a new certified Lycoming, Van's Aircraft, OEM for builders only:
http://www.vansaircraft.com/cgi-bin...577598-336-39&browse=engines&product=lycoming
Here are some other "name" brand builder, but no personal experience. They specialize in custom and modified engines:
http://www.bpaengines.com/
http://www.lycon.com/
Here are two others that seem to offer good service
http://www.eagleengines.com/Facilitengine.htm (N. California, I have talk to them and they seem very nice, customer oriented and capable.)
http://www.overhaul.com/pages/Eagle4320.htm
(The genuine Lyc option is more expensive but still it is an option)
(the above is in no way a complete list)
(Non certified come in two flavors ECI and Superior. You can buy ECI thru dealers like the above. Superior is also available thru dealers above but direct thru Superior. There is no advantage going direct and think it is less flexible way and may cost more.)
(Consider an engine kit where you get all the parts and assemble it yourself. This option saves money, but a complete assemble engines may be dyno tested and warrantied. However getting the engine disassembled may be easier if you are so inclined to build the engine up in the UK. As far as warranty it my be hard to get service once you leave the states. May be a local engine shop can build it and guarantee their workmanship.)
Shipping from the East coast to the UK may be easier?
If you have the pounds, I mean dollars you can have the engine.
Cheers, George