If you have the split flywheel then it is likely you should replace the rubber disks & re-set the pressure on these, there is an article in the members section for the PVT Cars which describes what to do, the replacement disks should be available from Brian Eacott & i believs Rod Briggs may be able to supply also.
I assume you have a PVT Engine block with whats called the 'Cats Paw' mounting, if this is the case you will now find enought room under the water inlet pipe to fit a modern viscus damper which would offer a better result.
The split flywheel effectively increases the combined resonance of the crankshaft/flywheel so increasing the RPM before the fundimental frequency of the crankshaft is reached, i would also expect ther is some damping effect also but not to the extent that modern crankshaft dampers can achieve.
Hope this assists.
Robin