i have an 85 308Qv and had the XDI installed about a month ago. My friend has a 77 carbed with XDI. Great system! Main tips are to follow Nick's suggestions, he KNOWS these systems. As for setting, i have mine at 10/25/0.5. Nick sets them at 10/30/-2 or thereabouts. The only real way to be sure of the settings is once installed go to a dyno and tune your idle first via the dyno's wideband 02 sensor. You want to aim for around 13. Once there you have them do a run and log the A/F. Adjust advance accordingly within sane parameters. Check your owners manual as around page 70 or so should be what the stock advance curve is. That should give you a nice ballpark figure.
Hope this helps.