Derek,
Many versions, P45's were from the early 80's maybe until 92-94 era, there was a long and short style sleeve. (first 2 pics)
Mid to late 90's the Picco exr versions came out, for the 45, 2 ring silver head, deep as in size was the bluehead, then a thin bluehead all hade the same piston/sleeve, a black head in 2000 was almost a complete different motor, still called an exr.
2009 or abouts, dark blue head, black head, even a red head in some other countries (Japan), this version was exr also , and almost every part interchanged with the 2000 45exr blackhead. The domed pistons I always machined flat.
I'll post some pics to add to the confusion.
The parts shown are for the 2000 45exr through 2012, Ill take any extras if you want to sell.