I recently purchased a 1955 Thunderbird 292 3 speed w. O/D.  The car is bone stock.   I have built many Ford hot rods over the years.  I haven't worked on a Y Block in years.  My plan is to remove the stock engine and put it in the corner of my garage so that any future owner can reinstall it if desired.  I have a complete 40,000 mile 1957 Ford 292 2V engine and a separate set of G heads from a 312.  A friend has a 1957 Holley pattern iron intake I can buy.  I'll probably run a single Holley carburetor.  My goal is to build a stock looking decent running street engine, not a racer.   I have a couple of questions please.

Are the combustion chambers bigger on the 312 heads?  Can I bolt them onto my 292 with stock pistons?  Any idea what the compression ratio will be?  I will be using the higher ratio 1957 rockers.  I plan to run an Isky .448 lift cam.  Will I have piston to valve clearance issues?  Should I convert this car to 12 volts?  Thanks for your help.