Sepp,
The 1998 (1851) cylinder will bolt right on to your bottom end, but you will need the power valve setup for the 98, as your 94 setup will not work. The 94 head will work on the 98 setup, but has a smaller squish width versus the 98, which can be better depending on what type of power you are looking for. As far as exhaust pipes, your 94 pipe will fit the 98 cylinder but the 98 has a smaller exhaust duct and so does the 98 exhaust pipe.
The 94 is a good setup stock, and is actually faster than the 98 IF ALL of your power valves are in good working order....
Hope this helps.
DoldGuy