I've had A15's that buzz no matter what you do. The only cure appears to be a harmonic balancer from a company here in Sydney called Ross Balancers. A friend of mine in Newcastle has done this & it cured his harmonics problem, which was due to a knife-edged crank. It could also be a broken valve spring, which will buzz & transmit noise through the car.

i am punching in the dark here... could it be you installed your piston backward? i did that once lol.

My wife was painfully translating and article at a book shop with A15 engines rebuilt on top of a tyre outdoors out in the wind and this was for 10,000rpm A gatta series competition.
A series comped cars only and the one in the article wasnt the only one using a stock A15 crank with spiffed up rods, pistons, head and the rest but the crank was left standard.

They are bullet proof engines and unfortunately we cant help much with that info.

Can you post a vid up using photobucket.com?

are your rods and pistons all -/+ 1g in weight from each other?

So many things could be causing this issue

The A-series engine is one of the smoothest 4-cylinder engines and Datsun did a precision balance at the factory. That being said, occasionally one will have a vibration issue. For example, if the flywheel bolts are loose, if a modified engine is not balanced correctly, or if one part is out of specification (e.g. a heavier than stock piston is replaced).

A cam won't cause a vibration when run in the RPM range it was designed for. A large-duration cam may shake at idle, but when revved up will be smooth.

Stock flywheel (unlightened) and stock type LUK clutch set. The flywheel and the pressure plate were balanced with the rest of the reciprocating assembly. No change in vibration when clutch is depressed.

Problem here is I have no frame of reference and no friends with A series engines. This is a simple 4 without a balance shaft. Maybe this is what happens when you stuff in a 262 duration, .425 lift cam. Just doing some research.

I only found a balancing problem in your wifes chicken FS recipe :)

whats your flywheel and clutch setup?

...only I don't have solid mounts.

Ah, so it is the normal race-car vibration. Nothing to worry about.

If you have ever been in a race car with solid mounts then you know the sort of vibration I am having. If the balance specs look OK, then I will investigate further when I pull the engine/trans out to rebuild the trans. I will also consult with the machinist at that time. It's a good shop and I am a repeat customer.

Engine has lots of power. No problem there.

The specs look OK.

What kind of vibration does it have, and when does it occur?