You are modifying both harnewsses. You are making the sr harness fit into the ka harness. The sr harness connectors don't fit the ka harness. So basically you are cutting off the sr harness connectors and replacing them with the ka connectors.
It's kinda hard to say, The question is why is it missing a headstud. I mean you can get a head stud but it take basically rebuilding the motor in which you would also have to reset the timing as well. It's kinda like killing 2 birds with one stone, but its a BIG stone to throw.This is how to basically take apart the sr motor down to the head studs.
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Make sure you get all of the old head gasket residue off the bottom of the head
So once you get to this point you get the old studs out or if the one stud is broken in the block then its gonna take some time to get it out. Your gonna need a bolt remover, (home depot) Then clean out the threads in the block to make sure that there is no gunk in them. Apply some assembly lube to the stud and hand tighten them into the block. and remember just hand tight.
Then install new head gasket, install head back on.Thread on the stud nuts and starting from the inside and working you way out (using a little oil on the nuts and threads) torque them down to 20ft/lbs. Then repeat the process starting from the inside and working out, 40ft/lbs. And then again to 60ft/lbs. And then 1 more time to 70-75 ft/lbs.
AND THEN install everything back on the motor(exhaust manifold, intake manifold and etc etc....)
SOOOOO there you go. If you think its worth all of that to you then grap a wrentch and get to it. The only good thing is that the motor won't be in the car which will make it easier to work on.