For the speedo is to use the electric sender from the tranny. I am toying with this myself. Everything else, oil, water temp, voltage the stock senders should be all you need. For the dash lights, you could trace the wires on the original harness and cluster to figure out what does what and use LED's or stock bulbs to frankenstein a functional gauge cluster together. My original idea was to build new exterior and just bypass everything I would replace but retain the stock turn signal indicators etc. Now this will probably wait until next year since the coilovers are going to drain most of my car fund this winter along with replacing hoses, adding dress up kit and redoing the brown interior black and massive rewiring stuff...
Hope this helps some.
Carl Auer - 82 FI X1/9 "Copperhead"
Seattle X1/9 member #50
Professional Photographer based in South Central Alaska