No need to go to a Gen 1 block. Keep your block.
Keep valves oem size, just swap to stainless, put heavy duty springs in the head.
The valves and springs are a must for sure. The remaining is dependant on how much you wanna push. If you're going beyond 15psi I'd definitely do the pistons and rods.
Back cutting the trans is really a good idea if you are going that far. If you are taking it to the strip and launching it off the 2 step, then do the HD output shaft on the trans. If you're just street riding and roll racing, then don't waste your money on it as it's not needed.
Your crank is fine, you don't need to upgrade it. Lots of huge hp bikes running the stock crank (me included).
Keep it simple, lots of people will tell you that you need this and that, but alot of the time you don't. You just need to know exactly what YOU are gonna do with it and that will dictate what you need.