Experimental engine question

Curious to know what engines cost, I was searching on eBay for o-360
engines and came across a listing for a Lycoming O-360-A1D
Experimental engine. I thought, since Lycoming's O-360's are used in
production airplanes, that these engines have to hold FAA non-
experimental status.

I know that there are engines that have not yet been certified by the
FAA, e.g. the Deltahawk Diesels, and some that never will be like the
Mazda 13B conversions. I am a little confused, however, about a well
known engine from a commercial airplane engine mfr carrying this
designation.

Can someone help me with understanding a little more about what this
"experimental" designation might mean?

(Actual listing:
http://cgi.ebay.com/ebaymotors/_Avia...7C24 0%3A1318)

Note that this is an expired listing so you'll have to have (or
register for) an eBay account to see it.