I have a BJ8, and I haven't removed the exhaust manifold in situ, but I think it's doable (I assume the engine's still in the car?). You'll need to get the car on a lift or at least jackstands; most of the work will be from underneath (be safe). You have to undo the nuts on the studs on the bottom flange to disconnect the down pipes; if your pipes' flexible sections are in good order you shouldn't have to pull the pipes out of the muffler. The nuts are likely brass and should come off fairly easily, but if you have to really torque on them you could snap a stud, which means you're committed to removing the manifold*; I use a ratchet with a couple long extensions and a deep socket. The top nuts on the studs on the head should be accessible, but I don't know about the bottom ones (you should be able to tell when you get under the car). Some of the nuts clamp both the exhaust and intake manifolds; I don't know if it's absolutely necessary to remove the intake manifold, but it would certainly make things easier. The hard part of getting the intake manifold off is getting the carburettors off, esp. the rear as the bottom nuts on studs are hard to get to; some of us have modified wrenches--1/2"--to make the chore a little easier (I use a 'stubby' wrench I got from Harbor Freight).
I don't have my shop manual handy, but I don't recall any instructions for R&Ring the manifolds; it's pretty self-evident what needs to be done.
EDIT: When reinstalling, check the manifold->downpipes and downpipes flanges. The manifold flanges can erode or even warp a little, sometimes making it difficult to get a good seal, and repop downpipes' flanges are sometimes installed erratically (flat-filing may be in order). The repop gaskets are failure-prone--since they can't use asbestos anymore--and I haven't had good luck with the brass nuts; double-nutting with steel nuts and a good anti-seize works for me. Use a high-temp sealant on the gasket for good measure.
* I broke one once with the engine in the car, but was able to get the stud out by MIG-welding a nut onto the remnants of the stud.