I have a fairly original 1966 CJ5. Original paint, original everything. I have made a few changes but nothing that is irreversible. I put in an SM-420 compound low transmission, 11" self adjusting, drilled drum front brakes, and adjustable oil pump and a gas can/spare carrier on the rear.
I also have a 2006 rubicon. I cut my jeep teeth on earlier jeeps than this 66 and have to say the rubi, in stock condition will out perform any modified CJ5 I have ever seen.
But I still like to hit the road and trails in the old 66 and it will still surprise me and a lot of others. But I like the old ones stock. Anyone can sink a ton of money into one of these old jeeps, but at the end, all you have is an old jeep with a narrow wheelbase, limited options and lots of maintainence.
Its for sale if anyone is interested.