Ebay has a set of pipes for the 600 twin, which will pep that sucker right up. 35-72 in about 2seconds from 5700-7200rpm.
Ski-doo flex skis bolt on with a couple spacers and and small piece machined out about the size of a dime on the one mount. They work great too.One not on the pipes Make sure you jet them correctly and take the time to get it right.
You change the headgasket to a smaller one with i believe 2 of the 3 layers (have not tried this mod but you can google it to get more info)
Also if you will be riding it on the trails and such you can swap the rear suspension with a Pro-action out of a newer yami, We just swapped an 96XT suspension in my dads to match my 96's
1996 Vmax 600 xt
GYT Twin Pipes
Bored 20 Over w/ Wiseco Pistons.
Camoplast 1" Track Un-Studded.
Suspension and clutches all inspected.
2002 Ski-doo Flex Skis