you gotta ream bushings to size. drilling isnt accurate.
ffs. you have to make sure things are square. you just screwed the simple step of drilling new stud holes! stop for a minute, breath deeply, say "ommm" then ENGAGE THE BRAIN. and it sounds like you did it to all of them. not one. four. ffs!
if the rod isnt square it will run for about five minutes then kaboom. waste of time by rushing on that part as well.
your main issue here is the bush will be 0.5 wall thickness... cant press it in, and it will be too thin and promptly fail.
those low temp rods are 98% zinc. 98% of carbs are made from zinc. so are nitto airline fittings. lots of things. it may be soft but it can take SOME load. just drill and tap the studs deeper and drill the holes undersize for a 90-95% thread depth rather than the standard tapping size drill.at least it would be homogenous if anything. jb welds just clinging there, and if you didnt thoroughly prep the case with acetone and sandblasting... its not going to cling there for long.
again. take a breath and ENGAGE BRAIN.
no. you cant drill a rod. its case hardened. if you did manage to drill it, you remove the hardened skin as well. and by square... i mean dead square. not close, not "good enough". 90 degrees. not 89 degrees,59 minutes and 99.8seconds... so i hope you have a milling machine with tight gibs and can make a decent jig to keep the rod square whilst you simply ream the bush, let alone try drilling the rod. doesnt sound like it. sorry. a hand drill is not suitable. neither is a dremel.
have you considered something different? like looking into rods from alternate engines? press the crank and replace the rod instead of creating more points to fail. have you looked at kx80 parts? yz 125s? anything?
sorry, but the way this thread is going i felt you needed a bit of a cold shower so you stop making silly mistakes...