On the tappets your referring to just the threaded bolt section that makes contact with the valve head correct? I considered just buying new rocker sets but If I take the rocker assembly out I will have to re torque the head again so I will have to buy new bolts and head gasket again as well. So the idea of just the tappers is very interesting to me. Thanks
Marlin himself does not buy new bolts, and if you rebuilt it with an aftermarket head gasket, you may as well replace it with an OEM gasket. Either way, to change the tappets or rockers (same thing), you have to pull the 'towers' off, because the rockers slide over the rocker shafts and there's no way to replace them without pulling it off. Replacing the adjuster screws won't do anything.
The 20-22R head bolts are not torque to yield, and Toyota does not advise replacement evertime the head is removed.
I have reused head bolts for years unless they are rusted, and then I replace them with used ones!
In todays world of fancy engines, almost ever engine uses torque to yield headbolts 
The machine shop was playing it safe when they told you to replace them. Look them over carefully, and if they look good, you know what I would do.
