The way I know for sure they are hydraulics is like Jerry said, they have a spring clip on the top of them and you can take them apart. Solid lifters are just machined hunks of metal with no moving parts. You can even shine a flashlight down a rocker rod hole and see if they are solids or hydraulic with the engine mostly assembled. The hydraulic lifters I get for these engines do not have 'trumpet heads', rather are the same size externally all the way up and down.

http://devestechnet.com/Home/Project1959235#hydrauliclifters


Deve

1950 Chevy 3100 Deluxe Cab
1950 Chevy 3100 Standard Cab
In the Stovebolt Gallery
The Think Tank
More info and tips at Deve's Technet