I've got an EL XR8 that only runs on ultimate 98 and has just had the thermostat replaced to run at a lower temp.
Can I get a smidgen more power out of it if I advance the timing and how do I do it?
A step by step run down for a dummy would do when you explain it.

Turn the dizzy anti clockwise a few degrees

I'm sure someone will be kind enough to list a step-by-step.

I did this to my I6 the other day, along with a bockle of Nulon octane booster (7 points along with BP98) and it made a bloody hooge difference. Changed it back soon after as the engine was hunting and surging and wouldn't idle that well.

Proper way to advance the timing is to put the EEC into diagnostics mode and then advance the timing probably by 2-4 degrees for premium. To put the EEC into diagnostics mode, short the top left hand pin on the diagnostics port (under the fuse panel in the cabin) to earth, then start the engine, it should idle and then rev and hold at around 2000rpm or so and that is when you check and change the timing, stock setting should be 30 degree BTDC.

Agreed. Timing marker is on the driver's side of the harmonic balancer, bloted to the timing cover. Timing degrees marked on the balancer itself...

As for actually changing the timing... while in diagnostic mode as described above.. get a 12mm (from memory, could be a 13mm) socket with lots of extensions, and get it on the clamp which holds the dizzy down, loosen it, and feel free to turn the dizzy.

Most people say to advance until it pings, and then back a notch... just be careful after, and listen for pinging carefully.

Oh, and don't forget to tighten that clamp bolt... like others did lol

Doubt you'll notice much difference, but doesn't hurt. Good luck!

Cheers