posi or no posi

[84 400]

Hello,
I have a 1984 and 1985 c-10's. my 1985 has 305/700r4/posi rear end in it. My 1984 has a new 400ci with th350 and ? rear in it (looks stock). I am wondering if my 1984 has a posi in it. I know it had a 305 stock in it then a 307 then a 383 and now the current 400ci(i have only owned it with the 400). The reason i ask is because when i was moving it out of the garadge yesterday, to wash it, and i put it inreverse to back it in i gave it alittle to much pedle and it left two black strips. However if i give it the pedle on the street it only leaves one. I know to look on the glove box sheet but mine is long gone on the 84. And if it is not a locker is it worth swapping the one from the 85? Thanks alot guys and gals(sorry about the spelling)

john
the first pic is of the 85
the next is of the old dodge(don't know why i added that)