Mike - Saw that small port on my unit. While the port tube was cast it was never drilled through into the housing. I stuck a drill bit in there and it is solid at the bottom. In other words blocked and nothing was ever hooked to it that I could tell. I made an assumption that the box was dual purpose and they either drilled it out for one purpose or left it as-is. I had the speedo gauge cluster out of my truck but didn't see anything there that vacuum would hook up to nor can I figure out - if it did - how that would actually work. The correction of speed would have to be accomplished in the mechanical cable somewhere between the speedometer and the transmission. Does that sound correct? Speedo does work but could not say if it is accurate in either high or low. Can you feed me a little bit more detail on this? Thanks
