of course dont forget to check the ground to the engine if u have a mulitmeter see if u get continuity from the starter housing to battery negative and check for resistance there should be none (ohms)

unfortunatly thats a clark with a mitsubishi engine i believe a 4g52 or 54 (or is it 53 i forget offhand) ithink the same model with a continental has a different designation than "mb"
mitsu engines sometimes when the ring-gear or starter pinion go bad they wont engage with eachother and u get a metalic thud almost a click with some oomph
first try moving the ring gear to a different position by turning the crank pulley or the torque converter (i dont think that tranny has a port to turn the torque converter like mitsu's do with the same engine)
take the starter back out and get a new 1 call helmar they have cheap replacements (look up their 1800 #) sometimes this works with a new starter pinion and closely inspect the ringgear when u have the starter out (with a flashlight)

good luck

That is a wonderful truck - there is a neutral switch after the ignition switch & a starter Relay also. Jump the starter solonoid from B+ then trace backwards most likely cause is starter relay.