If your 235/261 is equipped with hydraulic lifters, the adjustment procedure is the same, except you carefully adjust each valve to zero lash when it is in position, then give the adjusting screw 1/4 turn more and lock the nut. After all are done you must run the engine and whilst it is idling, adjust any valve that clatters only just enough to make it stop clattering.

Some folks will tell you to set zero lash then 1-1/2 turns more on the adjusting screw; this is wrong, and will result in misfiring and burned valves.

Be aware that the 235/261 engine design isn't good for installation of hydraulic lifters, and once the engine is fully broken in, the oil pressure at idle will not be sufficient to keep the lifters pumped up at idle, leading to clattering valves again. Later blocks have larger oil galleries in the lifter areas to provide the increased oil flow required by hydraulic lifters but normal hot idle oil pressure in these engines is under 20#; this isn't sufficient to keep the lifters pumped up.