Looking for thoughts and opinions from the vast Hudson brain trust.

Mine is the 1949 Commodore 8 with the 254cu engine running with an aluminum head. Milage is unknown as the odometer is not funtional and stays at 55k.  I was told by the previous owner that it was rebuilt some years ago.  My question is simply when will it need a rebuild?
The engines seems to run great as is and I don't want to fix what aint broke, but I don't want to be caught with a dead engine either.  
It seems to rattle a little, (valves?) uses probably a quart of oil every couple of full gas tanks (300-400 miles) but it seems to run out good as far as I can tell, having limited experience with these cars.  Cruises nicely at interstate speeds in overdrive. (70-75).  Although it has never ran hot at level highway speeds, even at high outside temps, 90(+-), I baby it somewhat and would never push it up long grades in too high of a gear.  I have taken it on several 100-150 mile trips in 90 degree temps with the guage never going over about 5/8.  It has never boiled over.  
With all this in mind, when do I need to think about a rebuild.  Rings, valves, etc.  
This car shows well and drives well.  I want to keep this car, and I want to keep driving it so I would like  to be pro-active about having a spare engine to replace the existing one rather than wait until the inevitable happens.I know what a problem these babbited bearings are to deal with.
Would a compression test on all the cylinders be handy?  If so what is the proper way to do this?
Thanks for your ideas and any recommendations.