Nick, 3/4 requires some fabrication ability and sound decision making.
Ideally, It's best applied to a narrow track sierra, or with the rear of a WT sierra converted to NT spring width. That's because NT's have the spring under the chassis which makes the conversion very much neater and cleaner.
Here's a photo of an opened up 3/4 on a narrow track chassis.
To do it like this you will need:
a set of 50mm wide trailer U bolts and spring plates
2X main leaves from a 50mm wide spring pack cut down
Longer shocks and custom shock mounts
relocate the fuel filler from under the chassis
Lots of grinding to remove the stock bumpstops and shackle hangers
That's about it. The fuel filler and the shocks and shock mounts are the hassle.
GRPABT1 has some photos of how to do it on a WT with stock spring spacing. IMHO though, I'd move the springs in if it was me.
Sorry for complicating things though - but I'd forget about the rear and RUF the front before I bothered with the rear. All the extra flex in the rear is only going to push the front end higher off the ground with the 5" of travel the stock front end has.
Here's a photo of a way bootyfab sierra that had MASSES of front wheeltravel and 3/4 rear. If that car was just 3/4 rear and stock front, it would probably be on it's side if tried to drive that spot.
It's all about the balance.
I'd vote more more travel in the front every time for a predictable, capable car.
Here's a car with RUF and OMe springs, shackles and bumpstop spacing in the rear. It doesn't have great rear travel at all, but the soft and flexy front makes it VERY capable.
with 33's
and another car with a similar setup.
3/4 rear might be a good solution for balancing the travel of RUF though.
Ruf is a lot of work, but if you are contemplating 3/4, you're already prepared to car your car up so don't rule it out.
Just my 2C.