Just dropping by for update, definitely not motor mounts. Checked from below with wife easing off the clutch w/ P-brake on.....that was her opportunity to take me out.
As for the belts, I did not take them off. The PS belt (first one to come off) is not the proper belt. The tensioner/adjuster (is it still called tensioner when there is no spring?) is completely relieved/loosened and belt is pretty tight on the pulleys. I considered prying/turning it off pulley, but didn't want to break it out on the street w/out replacement on hand as it wasn't in bad looking shape but is far from new looking.....probably should go buy two right ones and cut the wrong on there off. I considered removing brackets to get them off but my laziness got the best of me. I did however try to stick on component/pulley brackets method and listen to all components.....nothing seemed out of ordinary. Then I got distracted and noticed the clutch reservoir was has empty and figured the slave cylinder was going as I recently (6 months back) replaced master cylinder, and I know most people say do both at once or the slave will quickly fail afterwords. It was fine though so then I was wondering where my fluid was going.....I ended up chalking it up to poor seal on reservoir cap as after close inspection of lines, connections, and component pistons. I quit after this.
If I get some belts I'll try to create vibration with belts off and report back. I also plan to rebuild carb sometime in the near future....as it does run a little rich, I noticed a little hesitation also recently when taking off from start in the mornings, and the water temp choke thing is completely FUBARed. Once carb is rebuilt I'll check timing too.
Sorry to be rude Gnarls, regarding questions:
Did the vibration start suddenly or gradually? How many miles has it been there? 
I would look at the flywheel, clutch disc, and pressure plate. How many miles on the clutch, pressure plate, pilot bearing, and throw-out bearing?
It could be the pilot bearing has disintegrated, allowing the tip of the tranny input shaft to move perpendicular to the crankshaft. 
Onset of vibration: I can't comment on sudden or gradual. The truck has done it the past 40k miles which is the entire time I've owned it. It has not progressed though.
Mileage: at least 40k
Clutch and transmission/engine mating area: You know I keep thinking it's something in there too..... I don't know when the clutch was replaced, but I can tell whoever owned at one point in time cut corners here and there. The L52 was put in at somepoint along the way as I believe stock was L45. I wouldn't be surprised if whoever did not did not put in new pilot, throwout, and clutch. I really don't want to pull the transmission unless I know something is wrong in there. A little bit of chatter when it's cold or backing up a hill is not enough encouragement for me to dive in there.
Anymore simple/easy check ideas? Have a good weekend everyone
