hello all,
i am freshly back in a volvo after a couple years driving little hatches. I got my hands on a sweet 1984 with what I was told was a 1987 volvo 5 speed transmission conversion. when I picked the car up the owner and performer of the swap informed me that when he made the swap he lost the ability to use a cable speedometer, so he installed an aftermarket unit that is really just cobbed together and now inoperative. he alluded to the fact that in order to us a 1987 gauge cluster the whole rear end would need to be swapped? is that the case?

what did I get myself into? do I need to swap the rear diff in order to get an electric speedo sender to work for me?

what options are there in terms of alternate speedometer options?

the one he installed was an old vdo gauge that seems to work like the ones you put onto a bicycle (magnet on the drive shaft, readed mounted to take that signal and translate it to speed).

is it possible to simply remove the speedometer unit from the gauges and replace it with another unit?

thanks for reading my ramblings!