I would like to put an inline fuel filter on my 1979, but I was told you can't do it on a 1976 and later because special fuel filters with anti-spillage valves are used.
I have 2 questions,first what are anti spillage valves and secondly, where are they located?
Location: At my Bar drinking and wrenching in Lafayette Colorado
You don't need - or want - an in-line filter with a Q-Jet. The in-carb filter flows plenty and is all you need.
The filter in your carb has a checkvalve in it. This valve was originally intended to prevent fuel spillage in event of roll-over and fuel line rupture. It probably doesn't function too well in its intended role, but it does work well to prevent the common Q-Jet float bowl drainage when the car sits overnight.
Highly recommend you keep the in-carb filter and not use an in-line. Leave the in-line filters for the Holley and BG carb users who do not have in-carb systems.
(Point of interest trivia: Do you know that the stock in-carb paper filter will actually prevent sugar from getting into the engine if someone puts sugar in your fuel tank? The common in-line filters using filter screens will not stop sugar...)