I’ve built several Garrard’s for friends - both 301 & 401 - to very high specs.
I’ve also heard varying platters/bearings including CTC aluminium, CTC Brass, Shindo etc
401
Using an Audiograil refurbished 401 as a starting point with additional mods by myself including custom plinth I found the CTC 20mm larger aluminium platter with CTC bearing an improvement over standard. The heavy brass platter on the 401was a massive improvement over the aluminium - stability, precision - far more substantive sound with authority.
301
Here’s the rub. I don’t think the heavy platters work that well on 301’s. The reason is twofold - 401 motors have a lot more torque than the 301 and the 301 is more of a Rube Goldberg TT. The 401 is more neutral.
In terms of 301 motors they varied a lot from low to medium torque.
My own 301 is pretty tricked out - a number of improvements over and above the Artisan Fidelity/CTC 301’s.
As far as platters go - I started with a standard 301 strobe platter, had it precision machined flat to a few micron - I would not recommend this unless you have a engineer that has the skills to work to microns because it is very easy to remove too much meat and leave parts of the platter too thin in parts - the standard platters are not uniform thickness underneath.
I have the following mats in the cupboard - Boston 2 Graphite, Micro Seiki 180g copper, Final Audio 4.5kg copper, SAEC SS300 alloy mat, Goldmund Relief Mat/Clamp, Sota Compositions mat ( barium lead/acrylic ) and a few others.
Weights and clamps in the cupboard I have include Final 1.8kg weight, Audiocraft weight 75g/1.5kg, Goldmund Relief Clamp and several others.
Also tried Stillpoints weight ( horrible ), Origins Live mat and clamps - horrible.
I have found the heavier platters such as CTC and Shindo sound weightier and better in some ways but they upset the base timing and coherency. I believe this is due to the 301 being a Rube Goldberg contraption where changes can upset the balance and the motor is not as strong as in the 401.
I have also checked the wear on some of the heavy platter/new bearing combinations installed after a year or so and seen more wear on thrust pad and spindle than my original 50 year old bearing/spindle - there are no free lunches.
My recommendation would be to get the CTC 3mm thicker standard size platter - this will give you a flat surface to try mats without adding a huge amount of mass.
Personally in my own system I use the SAEC SS300 with no clamp or weight. This presents a more relaxed sound than other combinations but has the advantage of not loading up the bearing.
My bearing is modded - long CTC spindle in original bearing and modded thrust pad - I cannot recommend this because spindles and bearing housings need to be made in pairs. I started with the CTC spindle ( which fortunately was oversize ) and honed it down to match my original housing.
If you buy the CTC bearing to match the platter - get the long spindle version - this will enable you to experiment with thicker mats and weights clamps etc.
My modded 301 easily betters my old Platine Verdier - using the same arms/cartridges in comparisons in my system.
Aftermarket power supplies - you need one that can vary the speed. The Long Dog Audio fits that criteria.
One thing that I noticed after rebuilding my motor, including new bearings, precision matching the motor spindle, and using the best double ester oils for lubrication - my 301 ran way faster. Calculating the speed reduction required I tried the smallest ( Red ) CTC pulley that should have worked. Unfortunately their tolerances were out by some margin, so I had to trim the motor pulley by hand, individually for each speed to get the speed control centered.
What I surmise is that Garrard carried a stash of different sized pulleys for 301 production to accommodate the variability of the motors, and depending on speed, selected a pulley that got them there.
Even the positioning of the motor pulley can alter the speed - I have found some original pulleys are tapered - which means you must get the pulley in exactly the right position.
Using a separate power supply with speed control can bypass these problems.
On my 301 my speed is absolutely spot on on all speeds without the need for an aftermarket power supply. Using this as a base I have found well designed power supplies offer an improvement - but the biggest advantage is being able to dial in the speed accurately for most 301's that are not spot on.
As far as installing aftermarket bearings you can change the bearings without removing the TT from the plinth, and not turning the TT upside down quite easily - but it requires nimble fingers and small tools to get up inside underneath to the 3 nuts underneath.
Hope this helps.