I replaced the short allen head motor mount to frame bolts buried in the frame with 120 mm long bolts capturing a rubber cushion and washer under the frame. Biggest reason, I have spent a lot of time grinding off/drilling out stripped allen bolts at work, and buried in the frame like they are, original bolts would be inaccessible to a die grinder to cut them off. Also, since manual car doesn't have shock absorber mounts, a little additional rubber vibration isolation is a good thing. To buy these bolt one at a time cheaply, buy "gm starter bolt" from dorman "help" line. Of course, boxes of bolts are cheaper by the each. I've got some 1" thick x 6" wide rubber belting I use to make engine and transmission mounts, use a spade drill to drill holes in it.

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'80 240D biege "Mercey Bird"
'80 240D light blue "Slug"
'80 300SD dark blue "Theodin"