To answer your specific questions:
• First off, you are correct, the 114, 114a, & 114b all have Lycoming IO-540-T4 engines. The price of the AVGAS STC is $3/hp, so you are correct they all should be $780. Our website has been corrected to reflect this. The engines and airframes are listed in the following ways:
o 114 - IO-540-T4A5D & IO-540-T4B5D - both 260 hp
o 114a - IO-540-T4B5D - 260hp
o 114b - IO-540-T4B5 - 260hp
• Secondly, UL94 fuel is NOT approved on the Lycoming IO-580-B.
o For a list of Lycoming engines that are you can refer to Lycoming S.I. 1070, under the minimum fuel Grade UL91, here:
http://www.lycoming.com/Portals/0/techpublications/serviceinstructions/SI1070T Specified Fuels.pdf
• In general the issue of hardened valve seats is propagated by the engine OEM's. However, in all the testing conducted by Lycoming and the FAA on unleaded fuels in general - on all sorts of engines.
o You can read more about Lycomings' thoughts on what lead is in fuel for in section 2 of this publicly released document from Lycoming:
http://lycoming.com/Portals/0/UL 100 Avgas Flyer FA v3.pdf