There's a huge write up here on all the different heads in the Tech-Wiki here it is: A-Series Cylinder Heads.

The H95 is probably more ineffective than a stock round port head for racers as it has a huge restriction in the ports just at the major turn into the cylinders (okay that's probably an over-statement so don't take that one as gospel, but you get my drift). This was intended to create a swirl effect and it was used as an economy head. Don't try to port the H95 out to get rid of the restriction, you'll end up finding water, sooner than you think.

The H75 is commonly referred to as the low-comp head due to it's combustion characteristics (large open cylindrical chamber surrounding the typical kidney-shaped combustion chamber) and sometimes because it actually has 2cc's more in each chamber than the H89 or GX head.

The H95 is 29cc per combustion chamber from memory, might have to check that though.

I think ddgonzal posted a picture of about 6 different thermostat housings, some have a differing number of bolt holes but they all share at least two common holes in bolt pattern so you should be okay using the common type.