ok, i thought i was buying a 20r head with some mikuni side draft carbs bolted to it. well, i get home, the mikuni part was what it seemed obviously lol but to my surprise this head i have is deffinetly not a 20r head, perhaps its better. im not sure what the deal is, it has no markings other than "1.8" casted into the area under the cam. here is some pics of the combustion chambers. the head i bought has a shallower, as well as tighter chamber than a 22r. it also accepts a 22r intake. i also added a few pics for comparison. if anybody knows what this is i'd be very interested to know.
here is a 20r combustion chamber. looks similar to a 22r.

here is a 22 r combustion chamber off of a head in my shop that i know to be a stock unit from an 81-84 moto

here is the head i bought. notice how tight the combustion chamber is

 

i had the same head on a re-22 in an 87 toy and it is a high compression head from an engine in front of an auto 4x4

 

it should work with the older 11.280 deck height motors??