I use a fuel additive which cuts out the pinking; I've also removed the retard pipe from the distributor to the carbs which was part of the '70s emission system to get the Volvo through US emission tests.
Yeah, they are a thirsty bastard. I was getting about 18mpg out of mine when it was on the road. It needed super unleaded too (with additive obvs) or it'd pink like a twat under load. Not a cheap vehicle to run, but worth it as they're such a nice drive.
After doing that, setting the dwell angle and timing correctly, valve clearances, new carb diaphragms, points and plugs she does about 22mpg on average and approaching 30 on the m.way.
Since I've owned her (8 years ish) I've replaced the rear shocks with Bilsteins, had a bit of welding and painting done to the front valance and spare wheel wells, removed one of the 3 back boxes, replaced the rear mudflaps and located and replaced missing trim on the boot lip.
Underneath is tidy- very tidy, I believe they had a galvanised floor pan. Being a Volvo they have a roll bar just behind the sun roof and side impact bars on a '72- the first appearance of them I'm aware of.