The DUI is a blueprinted HEI "dizzy' (that's Aussie slang for distributor).
It uses weights and springs for the mechanical advance. You can get them with or without vacuum advance. Mine has the vacuum can, I even added an adjustable can to it. Never have figured it out.
Performance Distributor advocates 'power timing' rather than using a timing gun. They say timing mark are notorious for being off, especially with used harmonic balancers, because the rubber layer will slip over the years. They say set the timing conservative, and then keep bumping it up (advancing it) until it pings a little, then drop it back. Other gurus say don't ever make it ping, because a little damage results immediately. The best way is get a timing wheel to check the mark on the balancer, make sure zero is zero.
MIne is set conservatively, but when I shut the key off, the motor spins backwards. I have to be ready with the clutch. I haven't figured this out yet. They call it 'dieselling', but my compression is so low, I don't know why it happens. I've cranked all vacuum advance out, and it still does it. I'm stumped.