Oh thats easy if the head is off the lock just look at the combustion chamber shape. If the chamber shape is round in shape then it is a talldeck, or openchamber head. If the combustion chambers are a pear shape then you have the head from a shortdeck r series motor.
More info I found:
The short deck has a slightly lower block than the tall deck. (duh)
The short deck uses a 2 less links in the timing chain. 96 vs 98 links
I have been told that the 96 link single row chain can be upgraded to a double row by using a modified early 22R timing cover, oil pump, drive spline.
The 20R exhaust manifold had air injection that mounted on the manifold top and no oxygen sensor mount.
The 22R does not and some do and dont have an oxygen sensor mount.
The 20R exhuast manifold outlet has a single outlet into the exhuast pipe.
The 22R exhaust manifold had dual outlet.
The 20R exhaust manifold usually had 1 lower center mount stud.
The 22R exhaust manifold usually had 2 lower center mount studs.
Some early 22R exhaust manifolds had single lower center stud hole.
Some 22R exhaust manifolds had both configs of holes and had 3 holes.
Aftermarket exhuast manifolds usually fit all 20R/21R/22R by having all possible holes.
On some of that I'm not so sure, I think the 22R also had the air injection. Plus, after 20 years, who knows what has gotten swapped out....