Wouldn't it be esier to just buy one of the ultra-cool yellow on black R sport cluster for your car? Full gauges in one integrated package and a direct plug in except for the oil pressure sender. OK, not cheap but easier.
Anyway, the 242/244 difference does not mean tach/no tach as far as I know. Just an option. You do not have to go into the cluster wiring, nor should you, to add gauges. Other than the prewired tach. If you can't find the heavy shielded gray or black wire, just run one from +1 on the coil. that is it. For the other (post 80) gauges, "G" is sender, "+" comes from the fuse box and "-" is to the center ground.