Can the 3 way head be removed creating a level platform with a screw that fits a tripod socket?
On the U212, yes. Been awhile since I took the head off, but the mounting stud is either 3/8-16 or 1/4-20. Pretty sure the U212 includes a 3/8-16 to 1/4-20 adapter but if not, you can get the adapter for a couple of bucks.
If it's not a 3/8-16 it's 1/4-20; those are the standard sizes for tripods. 3/8-16 is pretty much the standard for mounting the head to the tripod, and 1/4-20 is the standard socket on all but the heaviest cameras.
I have a Manfrotto video head I use with my Slik U212 base for video work; it comes with the standard 3/8-16 threaded socket, and I recall having to use an adapter somewhere in there.
A clarification based on what
@vagrant said. . . the legs on the U212 can spread out almost fully horizontal, so you can get a stable platform on nearly any kind of terrain; of course, the more they're spread out the closer to ground the tripod head is, but the thing is wildly adjustable when needed. I've been using a U212 since my college days nearly 40 years ago and it's served me quite well.
UPDATE: There are several U212 tripods on eBay for very attractive prices right now. I'm tempted to buy another just so I have a spare.