All superjet motors have 3 basic pieces. The cylinder, and cases (top and bottom half).
90-93 Superjet - 6m6 (650cc) motor (single carb):
Cylinder = 6m6
Top Half = 6m6
Bottom Half = 6m6
94-95 Superjet and FX-1 - 61x (701cc) motor (single carb):
Cylinder = 61x
Top Half = 61x
Bottom Half = 6m6
96+ Superjet - 62t (701cc) motor (dual carb):
Cylinder = 61x
Top Half = 62t
Bottom Half = 6m6
The basic difference between the three motors is the top case half. The 61x cylinder is standard on all stock Superjet 701cc motors. The top case half of the 650 is similar to the 61x, but the 61x has larger reed cages and more flow. The 62t top half has even bigger reed cages and more flow potential.
For an average rec rider, a 61x is more than sufficient and easier to tune with only 1 carb. However, with a 62t motor the power potential is greater. If you are modding either motor with bolt ons (head, pipe, ignition) you won't notice much of a difference between the two. Once you get into case porting and aftermarket carbs etc, the 62t will outshine the 61x.
Basically, what I am saying is if you are planning a good budget ski to learn on, you don't necessarily NEED a 62t, but a 701 is a must.
EDIT: I started with a 650cc motor in my SN and rode it until my abilities exceeded that of the motor. Then I built a 701. So a 701 isn't a must to start, but you will QUICKLY lust for more power once you get comfortable on the ski.