The final revisions on the 301 would be the serial no's 80,000+ (black face plate oil bearing with 401 type platter)
But this is only half the story:
The early motors designed to turn the grease bearing (greater drag) and deal with carts tracking at 4g+have more torque and can run down to 90v effectively (hello Japan man) . The BBC changed their 301's from grease to oil bearings to cater to Stereo. Much of Garrards work on revising the unit was aimed at the motor and spindle bearings. -
In subsequent post production years it was discovered a great deal can be achieved from housing the 301 in the correct plinth.
In the ideal scenario: Late hammertone motor, oil bearing, detached motor to plinth, bearing supported.
Or oil bearing with very last version 401 motor (less torque but much quieter)
Purely from a sound perspective you would be looking at a mongrel.
Whilst much of the work is reversible, Grease bearing chassis need to be cut into (A la BBC) to allow for a Garrard 301 oil bearing to be fitted. The same is not true in reverse a grease bearing can be fitted to an oil bearing chassis. The debate between what sounds better grease or oil bearings is not clear cut, the motor windings are different and this is a key factor.
My life is tragic