I just found some info, I compiled a while back....
Later cams starting with 1954 powerglide and all later years used cast alloy iron cams versus older cams made from forged steel.
You can identify hydraulic from solid cams by finding the casting lumps, leftover from the casting process.
They are located on the rear of the cam between the 3rd and 2nd to the rearmost cam lobes.
2 or 4 raised lumps identify it as a hydraulic cam.
1 or 3 raised lumps make it a solid lifter cam.
No need to disassemble anything, just drop the pan and turn the engine until you see the lumps...
The later lifter designs were different from the earlier ones and don't interchange.
So if you identify a hydraulic cam you are good and just have to check what year your distributor is.
Part number can be found when removing the cap.
A few years ago, when I started overhauling my old 235, I knew little about cams and lifters.
I had some collapsed hydraulic lifters and just replaced all of them with a complete NOS set I found cheaply.
Pushrods turned freely and power increased slightly.
I still drive it daily ever since with no issues so far.
Maybe just luck, but the stock valve spring pressures are pretty low on these engines.
The problem is, good hydraulic lifters are harder to find these days and can be expensive.
Once you installed and broken them in on the old cam, you can't reuse them on a fresh cam, should something go wrong.
Although there are still cam grinders who recondition rare obsolete lifters and the critical convex hardened bottom surface.
