Wow, that's a hard one dude...
Why do you want to change the camshaft ? Is it a Tickford LPG system fitted or an aftermarket one that you can adjust? I'm guessing that you want to use a higher cam profile but I've never seen this done on a dual fuel car. My guess is this will give you a lot of headaches to get your engine timing right. Also the car will run leaner, which will make it backfire on LPG like there's no tomorrow, unless the system fitted is an aftermarket one that you can adjust to make it run richer, like an IMPCO or similar. If I were you I think I'll pick just one of the 2 fuels to run the car and then modify it. I remember fitting a camshaft many years ago to an EF but can't recall the part number. It was from Crow Cams and it gave the car noticeably more punch without screwing up the idle, maybe browse through their catalog and see if they still make them. No PCM upgrades were necessary.
There are many things you can do to your engine that will give you more power without all the dramas, like fitting a Tickford head (if you don't want to modify your own use EF XR6) or extractors or a hi-flow cat. Anyway, hope this helps. Good luck,