I am neither a pro, nor an exspert, but I have picked up some more or less good info here and there.
First of all, it is
not a P70, unless the top cover has been changed. The P70 came in march 1977, and your saw is older.
It also is not a R-series 85 or 100cc saw, as they would have weighted more than 19 lbs (like 21-22 lbs or so) with bar and chain.
I also think that all R-series 85 and 100 cc saws had air intakes in the top cover, like
this R40T, and your saw dont.
That leaves us with the 65 cc saws, even though the weight should have been more like 17 lbs with bar and chain, provided it has empty tanks and is clean. Maybe you weighted it on your fishing scale?
The 55 cc ones would have had less power than you state that it has.
As it is all yellow, it is not one of the semi-pro versions.
That leaves us with the R420, R420T (with Thyristor electronic ignition) or R421T (with exhaust heated handles and Thyristor). The pictures of the 420 and 420T at CSCC is not correct, they show a later semi-pro saw.
It ads up that it has
a bit (but not much) more power than the S-65, like about 4 hp at 8000 rpm.
Accurate info on the power of old Partners is difficult to find though.:bang:
I suggest that you weight the saw again, preferably without bar and chain, and with empty tanks - as I am a bit confused by the weight you stated.....
There is at least one more rather remote possibility in addition to those discussed above, but I will hold that back until the weight of the saw is confirmed. This post is long enough as kit is.