Rich, it is really not as bad as it looks. A lot of dawn dish detergent and elbow grease and you will have no more tranny oil after that. The O-ring change out is easy. Just make sure when you open the transmission up that you get all the gunk out of it before filling it up with new oil. I usually use mineral spirits in a sprayer or spray bottle and just keep rinsing the inner parts until the are all clean, the dry it and put the new 90 weight oil back in to keep anything from rusting if it is humid out. It helps if you have someone to hold the transmission in place while you put the oil back in, but you can do it alone.
You will need a new brake package. Dont put that one back on.
good luck
Steve