700 tranny out of an 86 305 is going into my 90 350. Are there any differences in the tranny like is the valve body any different and what do i need to make sure the mechanic knows so he knows what needs to be done. Also will the tail shafts interchange because i would like to keep my speedo and the 90 is electric speedo where as the 86 is cable driven

 

If it's an f-body trans, the tailhousing is the same.

your speedo gears & VSS will go right into it.

88 & newer 700s use a different valvebody setup and are considered superior to the 86 700s.

Everything will be bolt-in though, including TV cable, dipstick tube, and shift cable linkage.

Say hi to your mechanic.