It should hold 5 quarts. Often dipsticks were replaced with one from a different application (I know of at least 3 or 4 different boss style/locations for the 3 V8 series and Ford/Merc variations) and the dipsticks are different lengths. You might look at your dipstick and see if a previos owner might have filed or scribed a new line on the dipstick where 5 qts would be.

Not having a filter isn't necessarily a problem with these limited filtration flatheads - just make sure to change your oil frequently - say every 500 miles.

If you want a filter - the canisters show up frequently on ebay. You'll need the steel lines and be sure to include a restrictor to keep your oil pressure up. Filter element is available at any decent parts place.