Quite interesting.

Apologies if I missed it earlier in the tread, what are the two large diameter holes on the rocker cover? ( Or are those typical of buell covers? If so what cover them)

Yes, it's Buell rocker boxes.
I don't have part numbers at the moment but we do have a few pics of them installed on an XL1200R.
http://www.sportsterpedia.com/doku.p...ref:engmech05f

Those holes are the holes where the PCV valves are sticked in to release excessive air pressure from the engine housing.

cool thanks!

I've been charting (from parts books and others) Evo Sportster rocker boxes in the Sportsterpedia.
http://www.sportsterpedia.com/doku.p...:evo:engmech04

I've found that the 04-06 lower box was used as a replacement for select 91-03 models.
Selection is based off outside finish.
The 04 lower box (and all rubbermount lower boxes) have the extra screw boss for the plastic breather valve unit.
That also means in reverse that rubbermount owners that don't like the plastic breather valve units should be able to swap their top section for 91-03 middle spacers and top covers.
And use the pop-in rubber umbrella breather valve instead.
It'd be interesting to know if this has already been done (I assume it probably has).