Diesel, just a couple of quick tips:
the KR 250 is a 'Tandem'-twin, not a 'V'twin. a Tandem twin has 1 cylinder behind the other, on the KR's the rear cylinder sat higher then the front, this gave room for the gearbox to sit underneath. The first KR250's were out in Australia in the early-mid 80's, so any example you find now, unles it is in mint condition, is *almost* certainly going to need a freshen-up of the motor ( pistons, seals etc). These engines have 'rotary-valve' induction ie. the carbies feed through the *side* of the motor, not from the *rear* like a normal parallel twin 2-stroke ( think RD, RG, etc). Rotary valve induction was used by Kawaski for many years during the '70's on all sorts of 2-strokes, including their GP racers - 250 and 350. It is technically way better than piston-port or even reed-valve induction.
The KR-1 and KR1-S are parallel twins ie cylinders sit side-by-side. These are later models, and are definitely a better bet for what you want in a track bike. ( Get a good one, rip off the lights etc, and you are pretty much ready to go. )
Easy way to tell what you are looking at - the early KR250's had a 'staggered' exhaust system, one low, one high. The later KR1 and KR1S had a normal system, one pipe out each side at same level.
That one on e-bay looks pretty good

How Fast Do You Want To Spend ???
Simple tips for buying a 2-stroke - 1- make sure it starts easily, 2 - with not excessive amounts of blue smoke ( if you can still see the bike, thats not excessive

), 3 No loud rattle from bottom-end under load ( ie go for a test-fang).
cheers
I

2StrokesDave