Trans ?

I am going to reinstall my 3 sp trans for my 1950 ford. What gear oil should i use and is it better to change Gear oil with trans installed or not installed

thanks

 

80/90w gear oil has allways worked for me.....i would fill it before you install it but remember to tape off the tail shaft so it dosent come running out on ya when you go to install it. my .02.........................john

 

sounds good thanks