Having had a few things apart over the years, the next dumb thing I would look at as is stated it should be 5 quart... There's nothing holding the dipstick in but the bolt for the support bracket off of the intake manifold (pretty sure, don't remember exactly...). Next time you're under the thing, probably with the oil filter off since there's not much room there feel up around the base of the dipstick, there's a ring where it should meet against the block, if that's sitting proud of the block there's your problem... or just unbolt the dipstick tube wherever the support is and rotate it a little and see if it goes down any, if it does bend the support some to match back up to wherever it bolts on...
I mentioned the end of the dipstick because I had to replace mine with a junkyard dipstick at one point because the original was falling apart, it got really silly...
