The Rover-Landers of BC

Series III petrol 2.25L. Been quiet all these years. Suddenly top end noise that sounds like a tappet or louder. Checked tappet clearances, all good. Checked compression, good. Checked for exhaust leaks, ok. Checked for loose head bolts, ok. Is there a way to check for bent push rod before taking the rocker shaft off?

Yes!

1) Visually. Are they all lined up the same way as they approach the tappet?
2) With the valve fully closed you have 0.010 clearance, so rotate the push rod and see if it turns on it's axis (good), or swivels (bad), indicating a bend.
3) Easiest. Have a look at all the adjustment screws and see if one of them is turned in significantly more than all the rest. This could also indicate a stuck valve after you've adjusted the clearance; but you did a compression check to rule it out.
4) Use a stethoscope (or a long screwdriver) and listen around the motor to determine where the noise is coming from. If it is from the bottom of the block, you can be sure it isn't the push rod.
5) With the load off the rocker, tip it front to back and see how much movement it has. The rocker shaft wears out allowing the rockers to tip front to back and it makes quite a noise and makes it hard to get a proper 0.010 adjustment.

Thanks for the info! Discovered the VanIsle website, too -- very interesting. Down here in Washington, we really appreciate the activity in the BC clubs - perhaps see you at the NW Challenge!