What is your recommendation on upgrading a Linn LP

Actually many Users who can remember back to early 1980s models find that the Valhalla version has much to recommend it.
(The Valhalla is no longer supported by Linn so you can't buy one now BTW)
One way to get close to (or better) that performance is to buy the Hercules II AC PSU. It is an external supply so fairly easy to implement.

The only thing I would say about the Hercules is that it can be sluggish on startup and you should give the platter an assist to get it up to stable speed more quickly. Once it's running of course there is no need to switch off the motor - just flip LPs while the engine is running.
It's an art best perfected without a felt mat (use a Ringmat instead because it doesn't stick to the LP) ;^)

The 1980's Linns are keepers. I'd do whatever I could to keep mine going. I am original owner of my Linn Axis that continues to deliver the goods. I'll be keeping it still as long as is possible.

Get a VPI Prime with 3D arm....

The first thing I did to mine was to upgrade to an Origin Live DC drive. I waited and waited then finally made the switch. Kicked myself for waiting so long. You'll be amazed. I'm lucky to have a Linn tech less than an hour away. Even before I took it to him I did the switch myself. A huge improvement.

Linn with Ferrari drive or anything else is old school.