I know in my 170B there are nut plates behind the rear seat on the bulkhead that's at the forward edge of the baggage compartment that could be used for fixed shoulder harnesses. I haven't checked to see if they are there on my 180 but I imagine they are. Just check under the headliner. You'll probably have to loosen the screws that holds in one of the wire headliner retainers and look behind that.
Thanks Akair, I should have posted long ago on this topic. The mags were the culprit. Upon installing a new O/H set and new plugs, it ran like a top. Couldn't be happier with the performance.
I have the Burl's box. It's STC'd and seems to be doing it's job well. You'll love getting rid of the big battery, associated cable and other junk!
I think the weight difference is about 4 lbs between the old generator and the Plane power. In the process I got rid of an old oil dilution unit and associated tubing on the firewall which saved more weight. I've been really happy with the conversion, especially together with the firewall battery.