Actually after a bit of a re-think they're not sump plug bolts but blanking plugs from either the heads or intake manifold. They were in a box of bits from my old Trike engines and just assumed they were sump plug bolts but inspection shows them to be too small for that. Definitely Subaru though. Sorry for any confusion.

05 Speedmaster,Reverse Cone Shortys,Thunderbike AIR Kit,K&N Air Filter,Snorkel Removed,Dynojet Stage 1 Kit(126 main),Needle-Clip 1 From Bottom,42 Pilot,NGK Iridium Plugs,Progressive Springs,Hagon 2810's,Barnett Green Springs,TTP Safe-Start,MOSFET R/R