Originally Posted by pric

The best way is to get custom pistons. (Or machine the stock pistons)
If you are using E85 you really don't have to lower the CR, 10:1 should be alright.

You can use forged Conrods for a Honda H22 they have the same big and small end dimensions as the M103 and M104
but at 143mm they are a little shorter so the compression will end up at around 8,5:1 on the 104.980.
Forged conrods also have the advantage of being lighter then stock, that means less wear on the bearings at higher rpms.

From my little experience the headgasket, has no issues sealing the combustion chamber, but the water and oil passages tend to leak.
Good thing on the M104 is that a really big M12 bolt is used for head, which has the advantage of being a standard 1,75mm thread pitch.
So you can get off the shelf 12.9 allen head screws, torque them to 140Nm(~100ftlbs), and there shouldn't be any issues.