I have a 1988 GMC Sierra 1500 2WD. It has been modified with a 383 stroker motor and 700R trans. The person who owned it before me disconnected the gauges and put in a tach, oil pressure and water temp gauges. It has no speedometer. I want to install an aftermarket speedometer but have never done that. I have looked at a few like autometer and there are electric and mechanical ones. Which one do I need and how hard is it to install? What are the parts I need besides the gauge itself? Thanks.