'63 SS / 194 straight-6

Recently had the ENTIRE top end of my motor done: new fully rebuilt head and all internals, new exhaust manifold, new intake manifold, new carb, all gaskets & seals, thermostat & housing, etc.

During my 2nd day of break-in drving, on highway at 65 mph (2800 rpm) I started hearing loud tapping noice that came & went in degree of volume? Engine idling very shakey at next exit? The shop has my SS back and are troubleshooting to see what may be up......?

Any guesse as to where that tapping may be coming from? As I said, it will be loud and then taper off to not loud and then come back loud again.....? Also, I've run 20 / 50 for oil for the entire 7 years she's been my daily driver, but the shop who did my engine work put in 10 / 30.....
can that be causing something to tap loodly at highway speed?

THANKS FOR THE HELP !!!