IF it's the same as my '59, which it sounds like it is, this is how I did mine just recently...
Put the rubber on the truck first, then with a helper we started working the glass into the rubber with our fingers and a small flat screwdriver. Did it on a hot day in the sun (makes the rubber more pliable)
The toughest part is the small rubber that seals it up. The tool you get is crap! A relative of mine is a long time body man and he had a REAL install tool that worked much better. Lube up the small seal with plenty of dish soap!!
