Yes, you should just be able to disconnect the gas. You will probably want to clean out the fuel system as best you can, get the carb tuned as well as check the timing. You may need to regap your plugs too.
Hi, the numbers stamped on the corner of the cylinder head was misleading when trying to determined externally if the engine is large or small port because post 73 4V engines were small port with a cast 4bl manifold. If yours is original it will be 2V. For petrol based systems, any of the major manufacturers dual plane plenums will be ok, personally I have always had a good run with Edelbrocks if sticking with LPG then general consensus is stick with single plane. Regards ignition, steer away from rubbish like Pro Comp and no name eBay specials and stick with mainstream such as MSD or Mallory etc.... Summit are a great source...Enjoy!