When it comes to your speedo,........ Crawl under the car and check to be sure the speedo cable is conencted to the tranny. It's possible that the cable was not reconnected when the engine swap was performed. ( there are no wires involved at all for the speedo to operate. )
When it comes to your tach,..... Look at the oil pressure guage and see what it reads. If it says 40/80 than it was a V6 Tachometer. If your car has a V8 than it will need a tachometer with a 30/60 oil pressure gauge.
When swapping a V8 cable cluster for another V8 cable cluster - you do not have to change the TEMP or the OIL pressure sending unit you already have.