Only way to know if they have the aluminum rockers is to pop off the valve covers.
I have come to never assume what you think is in the used motors.
I had 2 same motors, same model numbers. One was the one more sought after,
the other was not.
As to your value. If a person is going to use one as a racer, they want
to know if the bore is round, and all the parts are there. The 14 has a
few parts that could be used, and the 18 is a nice motor for a racer, but
most folks who build them want to go with the 23HP engines. I have seen
a few of the 18HP motors sell for a few hundred, but they were also
able to be heard running before the sale. The 14 would be best for a grass
cutter. Value if running hundred or so, but this is for a running motor complete.
If you go to a mower shop and ask for prices, that will be doubled.
When you say it has plenty of compression, is that with a gauge, or turning it by hand?
Are the valves set to spec before testing? The less testing you do, or know about the
motors, the less asking price you can get. The more confident you are about it running,
the more they are worth. Running to a grass cutter, is not the same as a racer.
New rods, pistons, rings, gaskets....... is the bore straight, are the bearing surfaces good.
Did Ed King own it?
I search for deals, and pick up whole mowers for $50 with these motors in them.
Your market for sale is your deciding factor.