360 tappets

360 use hydraulic cam followers.
Rebuilding them is fairly easy - unless there is damage.

 

My 360 Spider was making tappets noise when I first got her. The PO had the car sitting in the cold NY weather for too long. I put some Marvel Mystery oil in her and drove it a few hundred miles before an oil change. The noise went away.

 

The only problem i think, given your description, is that the HCF, won't affect if the valve is closed when the cam lobe is off it.
That's all to do with the valve spring and if the valve seat is ok/clean so the valve can seal.

You could rotate the engine around to where Cyl-2 should have all valves closed and then do a leak down test.

 

If you want original Ferrari Valve Lifters/Tappets, you're SOL. It were me I'd use the above and determine via a leakdown if its the exhaust or intake valves. Then depending on which side of the cylinder, have your mechanic remove the timing belt, remove the camshaft and then rebuild the intake/exhaust lifter on that cylinder. If you do a search here it's not that hard. Need an ultrasonic bath/cleaner.

I secretly have a fantasy of using german VW 28.4mm lifters to rebuild my top end for like $200 but I haven't confirmed the specs...

Edit: Looks like Superformance might be able to help you out...

 

I agree lifter as the cause sounds peculiar.

Let’s be realistic can’t imagine more than one lifter being defective.

This is a 5 valve/cylinder engine. Maybe I’m wrong
but At cranking speed I can’t see how 1 of 3 intake, or 1 of 2 exhaust valves not opening fully would lower compression.

Valve guide I could see.


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My shop rebuilt the hydraulic lifters, new ones were not available.

 

I hope I don’t have that problem, I understand what you guys are talking about about as much as if it were in Russian.