You almost certainly have a stock 10 spline. 26 spline is a significant upgrade and not something you would find on mostly stock cars like yours. How to be sure? You have to pull the transmission.
the only way to really know james snover would be to pull the transmission. i dont think you can get a glimpse of the splines through the inspection cover
I would certainly try to look through the inspection hole. Its one bolt and very easy to get to, so its worth a shot. You don't have to try to count the splines either as its a night and day difference in the size of the spline, so if you can catch even a slight glimpse of it you'll know.
Doubt you can just by pulling cover. You might have to use a pry bar and "depress" the clutch fork to pull the fingers in, then you might see it. If not, you would have to unbolt the trans and slide it back an inch or two from the bell housing and then you can see.
on the 10 spline, each spline is probably 1/8" or a little more. the 2g spline, they are 1/16" or little less width.
And if you have owned the car since new, it is 10 spline. Wasn't a factory option