I'm going to guess that the invert elevation of the waste line is below the slab, are you sure that what you see "about 3' above the floor" isn't a cleanout?
Are there floor drains in your basement?
There should be no real issues, one thing to keep in mind: A lot of the style in the '60's was to have a 'banjo' type countertop that would extend over the top of a toilet tank, keep in mind that height if this is what you have.
Not sure where you live, but many of the larger 'cities' have organizations that would accept it for re-ctcleing. Habit for Humanity would I'm fairly sure. Be sure it is clean, it may take you a little effort to clean it up but the charitable type organizations would be greatfull.
Before you take the two nuts off and pick the toilet up, go out pick up two wax rings, one with the integral funnel looking thing and another just a wax ring. That way you can do the job at one time, be sure to clean as best you can the outlet on the bottom of the toilet of all the old wax ring...
About an 'oversised' waste line, this is NOT always a good thing. If the line is sized too far over you will not get the scrubbing effect needed to keep solids from settling in the line!
^^^Listen to these people^^^ save your self some grief!
The other 'cheaper' options are that for a reason, first cost savings are not always the best way to go, spend the little bit difference and years down the road you won't even think about it, ---if you choose the lesser units, you will...
Nailer, just one comment (ok, maybe two) the expansion tank on typical residence installations should be mounted in the upright position, not as shown in the detail. The reason is to not 'trap' water in the piping nor in the tank against the bladder if there is one.
The only time it could come back to 'bite' you would be if you were to sell the property. It could show up on an inspection, you'd most likely have to take it out.
Not hard to do at all. Be sure to clean all the old previous wax ring from the floor and bottom of the toilet. New wax rings and bolt it back down.
The draw back is that there will be a lip/self like area between the the new riser and the base of the existing reinstalled tiolet. These tend...
I hear ya, that's why I'm here and not there!
Hey Keith---we need more 'smilies"
^ ^^^ look, look, I posted the first complaint!:(
...Oh, crap, (a plumbing term) I'll be the first banned!