There are plenty of people here that are more knowledgeable than I...but I can give a start.
1st: Pictures are going to help a lot.
2nd: This website is helpful: Link Removed There's a lot of guitar stuff there but some general info too.
3rd: I'm pretty sure you are going to need to take the neck off. Taking the pick-guard and pickups out will help too.
4th. You can look for numbers to date parts on: the pots, the pickup, the neck heel, the pick-guard, as well as the head-stock.
5th: Don't be surprised if not all the dates match. You may have parts from '76-'81--or something--I believe.
6th: Looking at the neck pocket can tell you even more: refinished?, really a fender body?, etc.
I have a "'78 p-bass" as well. I really like the tone. Though 70's basses can have their drawbacks.
My pots are from '76, the pickups from '77, the neck stamp is '78. And it think there was some other number in there that said "79" but I forgot what part that was.