I don't care for the instant start on my brother's Hardbody. It was clattering till pressure got up. Told him to add some Lucas. Cured clatter.
The E has 'hydraulic lifters', well hydraulic cushioning of the rocker arms would be closer. Dirt or build up can block or limit the oil under pressure getting to them causing them to tic on start or constantly. Next time it's down a quart top off with ATF and drive for a few days. ATF is highly detergent and will loosen the gum deposits, then change the oil.... and filter. Probably wouldn't hurt to switch to 15W40 Rotella T or Chevron Delo 400. Both are 'light' diesel oils with high levels of ZDDT in their formula. Diesel oils have higher detergent levels than gas engine oils too. These are OLD engines are intended for higher ZDDP levels than are available in today's over the counter oils. ZDDP is slowly being phased out as it fucks up today's catalytic converters and new engines are all roller rocker and don't need it.
The hardbody tank is about the same size. I think its 15.8 gallons. As for the tach, take the old tach lead of the truck from the 2.2K ohm resistor and run it to the same wire from the power transistor that triggers the ground side of the coil.