No oil flow to valve train.

This vehicle has been sitting for many years after experiencing overheating problems. A few months ago after purchasing it, I took off the intake to clean it up and install new gaskets as the previous owner suspected it to have a bad seal. After putting it together, it ran great and got good oil flow but the transmission is shot which I found out later after the first test drive when I noticed it was leaking everywhere. I plan to replace that later. Well, what ended the test drive was two pushrods breaking in half and so I decided to pull off the heads and replace them with another refurbished set I had purchased elsewhere. I also got a new set of pushrods. After putting it all back together, it has a vacuum leak somewhere and the timing and carb need adjusted which I plan to do. However, while adjusting the timing, I realized after seeing smoke emanating from around the valve covers, I wanted to take them off to make sure I have enough oil flowing to the valve train. There wasn't a single drop. There is a leak near the oil pan which I also plan to take care of but after checking the oil level, it apparently isn't significant enough to have drained the oil. So with the right oil level and pressure, what could be causing this? I inspected the lifters and they all looked just fine but the block is from a 1971-73 Chevelle or like model vehicle and the heads are from a 70-71 corvette so I got pushrods for a '70 corvette therefore I can't imagine the pushrods would in some way block oil flow. Any help would be appreciated.