Speedo cable help on my 72

[Larry.sisk]

I recently installed a 350 engine (1986 model) and an automatic transmission (TH350) now I'm down to hooking up the fuel guage,speedometer neutral safety... The truck had a 327 with a 3speed on the floor which I removed can any of you guys give me some instruction on getting these other things working is it just a matter of finding the right speedo gear etc also the truck has a 6 lug rear end in it ( front has 5 lugs?) I guess that means that the diff or maybe just the axels have been changed , I'm just wondering also how to identify the diff any help on these issues will be appreciated