The flame trap itself is a small black canister about 1 1/2" long, with a small perforated insert inside. It is usually mounted very inconveniently about halfway down the inlet manifold, just above the oil separator. They are often neglegted because so fiddly to get at. A useful modification is to get some longer hoses and re-position it on top of the manifold. Then you can easily pull it apart and clean at each service.
The small pipe to the inlet manifold is very important, together with the brass nipple it fits on. The restriction hole is very small, so easily clogs up remarkably quickly. It is an important part of the crankcase breathing system, and affects engine running too because of the pre-determined quantity of air sucked in all the time.

The oil separator (breather box) should be there. Test it by putting a hose (I think 5/8 ID) over the nipple, removing the oil filler cap, and blowing by mouth through the hose. You should be able to blow through it easily and feel your breath come out the oil filler hole. If you can easily blow through it, don't replace it.
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Thanks everyone for all the information and advice, Doug C. 81 242 Brick Off Blocks, stock, B21F (non-Turbo), M46; 86 244, B230, 140k , auto.

Have a look in the 700-series FAQ's. I forget what it's under, but it was not too hard for me to find when I needed it.

A "breather box", maybe about 3"x3"x4", is attached to the crankcase side using several screws. This is approximately below the intake manifild's #2 port. Pretty far down.

A hose about 3/4" outside diam. rises from the breather box and comes up between the intake manifold and the valve cover. There you will find a fitting with a 3 way connection. One thinner vaccuum line goes to the intake manifold, the other thicker line goes to the side of the main air intake duct.

Th 3-way connector comes apart, you should find the flame trap inside. Older ones used metal, now it's plastic. Clean with carbeuretor cleaner. Also clean the hoses, and the small nipple on the intake manifold. Clean the breather box if you can get it off. You'll need patience and a rubber wrist.

I cleaned a breather box with a lot of carb and brake cleaner, and lots of shaking and tapping of the box. Poked screwdrivers inside to break up the crud. If a Volvo or import-parts dealer will sell a box for a fe $$, that would be a good purchase.