Gidday Wet Ones
The 2V CC heads work very well, and the C/R you’ve suggested will be right in the ball park.
LPG mixes range from 100% propane to a 50/50 mix of butane/propane and I’ve never had any detonation problems. Make sure your cooling system is spot on and try for a steady 160ºC.
The stock electronic dissy will be fine, but be sure to have it recurved to suit gas, (total advance in before 2500-2600 RPM). I also fitted a set of decent leads (ICE) to combat cross-fire issues. Have a look at your engine running in the dark. It can be a real eye-opener.
I note that your diff is running 3.5 gears. What is the height of your tyres?
Here is a little calculator I put together for determining revs at cruise, and desired red line peaks.
Click here to download my Calculator v2
I had a similar combo and was very happy with the result. I took a lot of time choosing a cam profile and ended up with an old Cam Dynamics profile, part number 972227 (now badged under the Crane - Blue Racer logo). It had heaps of torque and maxed out about 4500 – 5000 which suits the limit of the 425.
(on page 17)
Here’s a bit of dribble that you might find useful . . .