Good point. If it's a stock engine without many modifications and a mild cam, the non adjustables are fine. If you upset the apple cart with changes, you will need to measure and get the right pushrods. Using adjustables on a stock/mild engine won't gain you any horsepower, or very little.I installed a hydraulic camshaft in my 1965 273 engine, a fairly mild "RV/Torque" camshaft (still has slightly more intake lift than factory HiPo camshaft, I recall). I bought standard pushrods for the 1970's 340 TA engine, which are similar ball & cup type as my factory pushrods, but just shorter to fit the hydraulic lifters. Might work for others using fairly standard parts like heads which haven't been milled much.