Steve, unless you want a show car and want to do nothing to it, a clutch isn't that big a deal to change on these things.
I'd recommend that you concentrate on the frame and the condition of the body. These two are the biggest expense and the most trouble to repair. Especially the frame...
As has already been said, the rear suspension where the A-arms attach is the biggest spot. The other thing to consider is the weak point where the diff attaches to the frame - check for a clunk as you change gear.
Other common rust spots include under the battery (check very carefully if they have put a tray in) and the footwells. You can see this better from underneath - it starts right where the floor ties to the bulkhead. The sills and inners you'll check anyway I'm sure.
A good test for originality (and bodges) is the seam between where the rear wings meet the deck lid. On an honest car there is a gap. If this has been filled and painted, check VERY carefully for rust.
The engine isn't inexpensive, but assuming it starts and runs ok, a compression and leakdown test will tell you pretty much what you need to know. Expect some minor oil leaks underneath - where the engine and box meet up is a favorite.
The electrics can be a pita. DPOs LOVE electrics. Especially check to make sure the reverse lights are working - if not tracing and fixing will give you fits - the switch is a bugger to get to without taking stuff apart.
Just like with the MG, everything is available, so parts aren't an issue. The only other thing I'd say is that if you like it and you have trouble fitting (I'm 6'2 and 245lbs) a smaller than stock wheel does wonders for the legroom...
You didn't say what year and whether it's an o/d or not. If it is o/d then they changed over in 73. The earlier ones are a bit harder to break, but both are a good thing to have (like arguably adding $1500+ to the value of the car). They are expensive to rebuild though, so make sure it works if it is there, and if it doesn't price accordingly.
If you come up with a year, I'm sure you can get some more specialised advice.