Easy open frames started around serial number 195,000 for the blued Contenders - all stainless frames are easy open. I prefer pre-fire frames to post-fire... because I don't like a breech face change they made later on (due to their crappy quality control since the fire and problems the mod can cause), or the hen scratch on the side plates of the P/F that look like a 6 year old did them.
Barrels are interchangeable, blued, Armor Alloy and stainless. The AA needs fitting, and ideally the barrel lug bolt(s) should be "matched" to your frame with all barrels. On the old stepped lug and solid bolt barrels you'll want to fit split barrel lug bolts most likely.
Be careful buying used frames - there is a lot of stretched frames out there, and very often the seller doesn't even know he's selling junk. When you do get your "C" frame, best bet is to have it checked out and tuned by Jim Henry in Barstow, CA. Prices are very conservative, and he's THE Contender Guru, way better than anyone they have working at the factory. I have his contact info if you need it (or of any of the aftermarket custom barrels makers as well). With over 33 years in using Contenders, will be glad to help in any way Dr. Mike.
Kiss your loved ones goodbye - you won't be seeing much of them anymore once the TC Wildcat Bug bites you. :wink:
Ladobe