Buy the northland shooters supply wrench and it is cut with a relief for the lug,and get his barrel nut wrench.Since you are a mechanic you know the value of tools for the right job. Oak blocks may work but I wouldnt count on it,go with the correct reciver wrench and nut wrench and you are set for life.If you dont want to leave reciever wrench marks on the reciever use the nylon strapping material they use these days and cut 2 strips slightly shorter than the diameter so it doesnt bunch up and add chalk or rosin as I do and tighten it up snug,dont kill it but just good and snug and use your nut wrench with a steel hammer to shock the barrel nut which the factory puts on way too tight.When retightening the new nut or original tighten it tight by hand and use a deadblow hammer to give a medium rap with that hammer and its good.It doesnt have to be 100 foot pounds to make it safe.