First off, see if there's a 1/4" thick shim between the crank case and head. If no shim, look for marring on the head bolts. If no shim and the bolts look untouched, it's probably still stock.
BTW, for the future, you should never buy a used sled without a compression test. It's a $15 tool and 10 minutes of your time to save you major $$$ and headaches. Cylinders should be close to 120psi each.
Shim would be between the crankcase and the cylinder block, not the head.
My opinion FWIW:
While I agree on the value of a compression test in general, gauges vary and elevation / barometric pressure has an effect as well so you would need to compare the values to a known standard, such as using the same gauge on the same model sled with a known recent rebuild, or the same sled over time.
A compression test does not tell everything. The piston skirts can still collapse some over time and use and possibly develop cracks without affecting compression, and the cylinder skirts (which are thinner on 2012 and older 800's) can crack from piston slap and you won't know it until it fails catastrophically. Fix kits aren't a guarantee, pistons still wear out over time, and some fix kits and pistons are better than others, and a cracked cylinder skirt can still happen, just less likely.
I would look for the shim under the cylinder block, run a comp test (and find a stock sled of same vintage to compare it to if possible). If comp is good and a shim is there I would run it and test comp every 3 or 4 rides, and keep a record of the results (same gauge every time, engine at the same temp either cold or warmed up every time). Watch for changes and inconsistency from one cyl to the other.
If there is no shim and studs do not look like the engine has ever been opened, or compression is questionable, putting new pistons in (with fix kit) and inspecting the cylinder skirts for cracks is cheap insurance compared to a piston or cylinder skirt going through the bottom of the crankcase... 500 bucks or so vs. a couple grand or more for a complete motor. Some pre-2013 motors run a long time, there is no predicting which motors will fail when, to me pistons are a maintenance item in a high performance 2 stroke motor no matter the brand. Had a buddy look in through the exhaust ports on his 800 motor and even though it was fairly low miles and compression was fine there was a fine crack in his piston... fix kit went in before the next ride.
