nook
+1y
There are 2 different R versions, in the beginning 75, the 20R was a tall deck, tall head design, used a dual row timing chain setup, in 81 the 22r came along, still the TD/TH design, and still had the dual chain set, around 82 they started using a single row chain with the same TD/TH. About mid 84 they came out with the newer version or lazer block as many refer to, it had a shorter deck, shorter head, and used a shorter single row chain setup, they won't interchange between the two versions. The timing cover was shallower, used a different oil pump and oil pump drive spline, and also the valve cover was changed to the coffin style square nose.
Depending on what year dual chain setup you have will determine which model engine it will fit. LC does make a dual chain conversion kit for the later engines, it is basically an early timing cover remilled to the shorter deck height, the top bolt holes filled and redrilled, uses the early dual row timing components, oil pump, and drive spline but requires a custom chain because of the shorter deck height.
If memeory serves me right, been a while since I counted them, but the early engines used a 98 link chain and the later a 96 link, don't quote me on that, but should be close. Also if you use the dual chain with the later square nose valve cover it will require trimming inside on the oil deflector for clearance, the older bull nose covers fit with no mods.
Hope this helps. PS. make sure to use some blue loctite on the adjustment bolts on the adjustable gear to keep from eating one down the timing cover after dialing in the camshaft.