Volvo Problem Solver. it gives the directions for setting the CO with a Dwell Meter and also for setting it at the O2 using a Digital Volt Meter, all in a single page.

Great compilation of Tech tips written by and for working Volvo mechanics...covering older models. Out of Print sold by IPD and Volvo parts providers in the way back for $65 --- printed before lazer printers tho so digrams are primitive computer stuff----But the Info is the best.

Go to: http://volvowiringdiagrams.com/

scroll and look inside the Trouble Shooting Guides Folder
Download: Volvo Problem Solver Advanced Edition-1.pdf

If you replace the O2 you will have to reset the CO using that adjuster.
If your Dwell Meter really only has an 8cyl setting then use a DigVolt meter to take the reading off the lead to the O2 Sens....see the same page in the ProbSolver.


Also--- you say your dwell meter only reads 8 cyl....???

what kind of meter is that...all Dwell Meters I've ever seen should have a switch that the meter to read 4cyl, 6cyl, or 8cyl.
Dwell meters are old school tech devices designed to set the point gap on engines with points-condensor ignitions. Most are dual meters so called Tach/Dwell meters that can be switched to read either Dwell or RPMs.

Your CAT may be causing the smell. But until you sort out the rich/Lean and other maintanence tweeking and take it for a run on the highway you won't know.