Technically a 70 Riv engine rated 370 hp 510 ft lbs torque. I believe it may be essentially the same as the 70 SR which in a lighter car was rated 350hp which is probaly more like it since we know that the SS code 1970 Stage 1 was rated 360 hp but on the factory dyno was about 376. The point is that the ratings were fudged a bit --sometimes up and sometimes down.
SF would probably be a bit higher in HP compared to an SR motor simply due to the fact the SF had the same compression ratio as an SS. SF & SS 10.5:1 SR 10.0:1
I think it is accepted that the CRs were inaccurate then too in the sense they seem to overstate the CR. I am not saying he is right but Dove's book has the SR and SF at 10 to 1 and only the SS at 10.25 to 1.
You can look at the compression issue between the sf, sr, and ss like this: Same block Same pistons Same stroke Same heads Different valves (SS had Stage 1's). Thus, it makes sense that the SS would have a touch more compression due to the valves larger size taking up a little bit more of the combustion chamber space.
Of course you are right Frank. It would have been more accurate to say they were installed in big cars like Rivs, Estate wagons, Electras, etc. The thrust of by post was to point out that if you accept Denns Manner's dyno tape of 376 hp at the factory for a big valve SS code engine it would be hard to accept the accuracy of a 370 hp rating for an identical small valve engine like a SF.
