I don't have Haynes yet. I used the Brickboard and Bentley. You can still run the test of the breather box. Hook the hose to the nibble an blow by mouth. It really doesn't matter if you can feel it through the valve cover hole. If you can blow through it, it's clear. With a new box, you can blow through really easily. If it's not easy to blow through, I'd replace it or at least take it off and clean it. It's very buried as you know. (When I first got the manifold off, I started using French when I saw what a rat's nest is under there!) I didn't want to leave any gunk in the box at all so I bought a new one with a new o-ring and replaced it.

While you're in their, clean everything in sight, and replace every single vacuum line you can find. I labeled everything with descriptions of where each line goes, etc., rather than risk messing things up. I found it helpful to remove the starter, too. At least loosen the three bolts that hold the fuel distributor and gently pull it toward the driver's fender and support it there somehow. You don't have to remove the bolts. The fuel distributor is mounted in rubber. Once it's moved, you'll finally be able to see the whole breather box.

It's also sensible to look at the sensors that are on the head under the manifold and consider replacing them. I replaced the center one which is the temp. gauge sender($6). The front one under #1 cylinder is the Engine Coolant Temp Sensor (ECT, I think it's called). The rear one I believe is the thermo-time switch which controls the cold-start injector. Bentley has descriptions of how to test. Groton sells Bosch versions of the ECT and thermal time switch I think. The center and rear ones would be ridiculously difficult to replace with the manifold in place.

Don't forget the heater core hoses. I did those also while in there.

Needless to say this job, which started as a flame trap cleaning, ended up taking much longer that cleaning the flame trap. (I don't even want to say how long.) My breather box was completely clogged! Now that I have the wiring harness, I'll be going in again, this time with less looking, less studying, and knowing that at least the hoses, vacuum lines, injector seals, breather box, and flame trap relocation are done. I'll go straight for the thermo-time switch and the wiring harness.
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Thanks to everyone for the help, Doug C. 81 242 Brick Off Blocks, stock, M46; 86 240, 130K