>>The front end seems fairly straight forward (pun partially intended) & there is a Racetech re-valve available as well as some documented fork swaps out there.
The Racetech stuff is works well but if you do a fork swap you get all the benefits of the more modern design: better stiffness, usually more rigid axle connection, and a well designed fully adjustable damping system. That's what I would do in your place.
>>I am wondering about fitting a WR/YZ shock to the back & this is where my question comes in. The suspensions seem very similar to me, shocks seem to be about the same length, orientation, etc. BUT the linkages between the frame, shock & swingarm are backwards from each other..
You'd be surprised at how similar the actual wheel rates are for link systems that look completely different. The main constraint for a rear suspension is packaging (fitting it in the available space) so there end up being a lot of ways of achieving the same thing.
The first major battle of finding a shock to fit seem to have already been won.
The second item to consider is the overall travel of the shock and wheel. If both measurements for both bikes are similar (+/- 1/4" on the shock, +/-1/2" on the wheel) then you are pretty close so bolt it on and see how the ride is.
If the wheel/shock travel are not that similar than you will most likely have to respring it to get the static and laden sag set properly. You can see how to set sag at http://racetech.com/page/id/30#2
Once you get it sprung properly then you may have moved the damping needs beyond the range of the 'clickers'. Only a test ride will tell you this. To get the damping adjustment back in the middle of the adjustment range someone will have to go in and change the shims and maybe piston. This is not a big deal and any suspension tuner will have the tools and parts to do it.
In general dampers are very stupid devices. They only respond to the speed of the movement of the shock (or fork) shaft. They have no idea if they are connected to a cantilever, linkage or whatever style suspension. The result of this is that if the wheel and damper travels and approx weight of the bike are about the same then the damper will be close enough to try out.
Good luck, let us know how it works out.