@Blueflame......
If you do decide to use a compression changeover valve, you must also adjust the bump clearance.
I have a JKSON too. Listeroids without the changeover valve use a different bump clearance, and it makes a big difference.
Wish I had one installed now, it's been -12 for days, Lizzie sits outside, and is reluctant to start without a bit of heat down her throat. When it gets a bit warmer, no problem.
Cheers
Hugh