Jonno
A Progressive is a 2 barrel "progressive". The first barrel works up to say 3500 revs and then the 2nd barrel cuts in. Both barrels feed into the one manifold. So the 2 barrels feed all 4 pots. The 2 barrels should face North South and the cable connects on the side. Also in tiny print on the base it should say something like DFAV 32/36
An IDF is a 2 barrel "non progressive" The 2 barrels are not connected. One barrel feeds the 2 left pot and one barrel feeds the right 2 pots. The 2 barrels should face East West and the cable comes through the middle. Also in tiny print on the base it should say something like IDF 40.
Make up your own mind as to your mileage. Make sure you odometer is reading the miles properly. Drive over a known length of road (those highway 5 k testers are very good) and measure against the odometer. Mine reads about 10-15% low!
Measure a couple of tanks as to what you get out of it. Dont expect miracles. I get about 8.5km/L in the city and say 12km/L on the highway - had "up to" 15km/L on a highway cruise to Sydney / Newcastle / Woolongong / Sydney
If your worried you are going to have to learn about jetting the sucker - you cant just take it to someone - way too expensive. Plus it is relatively easy
Have a read here and see what you have
http://www.redlineweber.com/Redline.htm
[Edited on 9-9-2002 by blue74l]