The Liquifire's heads reduce the effective compression ratio from the Invaders 7.3 to 1 down to 6.9 to 1...not a huge deal.....but sacrificing 3-4 ?? HP.
The Liquifire's stock jetting (at sea level to 4000 feet) is 150 Main jets, 110 (PTO) and 105 (MAG) power jets.....awfully close to the Invaders stock 150 Mains, and 120 power jets.
That small difference in jetting may, or may not, be due to the slightly different compression.
It could also be due to the slightly different air box design and exhaust system that John Deere engineered to fit in their Liquifire chassis., and the way all of those components work together.
I could find only find one reference for timing in my John Deere manual, and that was to "Align Stator Marks".
One would think you could advance the timing a couple degrees when you reduce the compression ratio, but I wouldn't even attempt it.. unless....maybe.... I could do all of this with the engine on a dynamometer.
I second gixxer6..... leave the timing as is, and run the stock Invader jetting.