I've been dynamic prop balancing for 15 years.

0.3 plus a little is not a severe vibration but could be improved.
Many skeptics would call it smooth to begin with.
What was the IPS amplitude of the engine aft,.... or did the operator just
use a single sensor? A sensor on the rear will give you an idea of
crankshaft and rod balance. Lycomings usually are 0.15 to 0.18 the rear.
If it was a custom balanced engine, the rear should run just as fine as the
front.

I'vd balanced some by placing correction weight on a Lycoming ring gear but
have gotten away from that method because it statistically takes far greater
weight per unit of correction. About 30% -50% more than if the correction
weight is placed on the spinner bulkhead, or if the prop's static weights
are adjusted.
Also, the method works less well on props with extensions.

I looked at the mooneymite site. Interesting. The same principle as a
reed tach. Its just a pendulum adjusted to resonance. Insturment face
vibration frequency will be at crankspeed, 1/2 crankspeed or some other
multiple half order.
The author is painting the tips, which will change the spanwise balance but
not chordwise balance.

I don't have the data handy anymore, but as I recall a long ago experiment,
10 square inches of painted tip needed about 11 mils of paint thickness to
weigh one gram. Can't remember what paint Iused, proably Krylon.
On a 76" inch prop, this means a 36 gram-inch balance correction which
will be about a 0.20 IPS.
Actually, one would probably have just as good luck in trial & error by
adding washers under spinner screws systematically. Or if you had some way
to measure engine movement, some sort of overhanging dial indicator, one can
easily find the solution by plotting a 3 way polar chart.

Take Care
Kent Felkins
Tulsa