[dsraven]

LG, personally I would think hard on whether or not to install anything below the dash on the left side. I had something down there on an old truck, a hand throttle possibly?, and recall banging my leg on it a few times. it seemed like a good idea at the time but it seems like when you like something enough in the planning mode your brain makes you move differently than normal when you are mocking it up. then you fab stuff and mount it but at some point down the road practicality sets in and wham, sore knee from impact.
I kinda like the tach to be somewhere it is easily seen, possibly overhead would work better than down by the knee but it seems like the gauge would still be small so not easy for eye to find in a hurry. I realise your cluster is likely completed and you've been driving for awhile but thats the spot that I would put the tach. maybe substitute a volt or amp gauge for a tach there and put the other gauge overhead. one that you need but don't look at a whole lot. just my view, everybody is different (especially me, according to the wife. haha)