The JAA list of aeroplane types, split into MPA and SPA can be found
here. If the type is not listed as MPA it is unlikely that hours on that type will be accepted except as PIC.
It is the manufacturer and/or the certificating Authority that decides whether an aeroplane is classed as MPA or SPA - it does not, necessarily, depend solely on weight. An operator can elect to operate any aeroplane with two pilots, whether certified as SPA or MPA - it is up to the licensing Authority to decide whether to accept P2 hours gained in a single-pilot aeroplane. The UK CAA will normally accept P2 hours provided that the relevant company Operations Manual requires that
all flying, including test flights and positioning, is conducted multi-pilot.