i have fixed the original bolt style hubs 2 different ways in the past. one: i used screw in studs [2 or 3" long depending on use] for aftermarket rear axles with the thin hex head or the allen style cap screw head. these were used with a drop or two of red or blue loctite. of course, the original threads were in perfect shape in the hub, plus they were both right hand thread hubs. second method was to fit for press in studs. carefully measure for the amount of thread needed for your wheel. if using thick center wheels, make sure the studs used have enough thread length to provide proper thread engagement with the nuts required for the wheels without bottoming out on the inside of the nut before the wheels torque to proper spec. if using open ended lugs, this isn't required to be looked at. next,measure the thickness of your hub or your hub/drum assembly. this will determine how long the stud knurl will need to be. make sure the knurl does not protrude more than about .010-.015" beyond the face of the assembly used because this could cause interference with the wheel sitting flat on the hub. flush, or below, is best for the knurl length. now you are ready to choose your studs. check aftermarket choices or look at the dorman catalog, and choose a stud that fits your requirements and has at least .015-.020 more diameter than your hole size in your hub[or hub/drum assembly]. for example, if you just drill out your hub threads to 1/2" to just remove the existing threads, you need a stud knurl diameter of .515" for proper press fit. if choosing other stud knurl diameters, open the stud holes to .015-.020 LESS than the knurl of your studs. this must be done on a drill press to insure your studs go in straight. next, remember to support your hub properly when the studs are pressed in to make sure, after all this, you don't bend your hub or hub/drum assembly. all this blabbing may sound like this is a major undertaking, but it is just a very simple job.
i'm glad no major damage other than a tire was caused, but i question the use of just straight bolts to secure your wheels to the hubs. i have never seen any brand of slot mag that had a 1/2" hole used with the proper nuts. they were either a shank style[most common was the 11/16" shank size] or an acorn[stock taper] style nut. if i remember, those used a 60* taper. i could be wrong, but i think you are looking at a very bad deal using straight bolts on those wheels even if you use a washer that fits inside the shank hole. just my opinion, but i think it would be best if you repair your hub/drum properly asap, or convert to disc brakes, which would be the best way to go. and before i close, if your drums are riveted to the hub, does your wheels have reliefs in them that the rivets fit into, or are the wheels just sitting on the rivet heads ? if so, that is very unsafe as well because the wheel will not have the proper support on the mounting flange, which can lead to cracking of the center. i bring this up because i have seen the results of this happen many years ago when a friend of mine bolted on a set of slot wheels on a 35 plymouth 4dr. sedan using just longer 1/2" bolts and sitting on the rivet heads. this resulted in the center breaking out of the wheel instead of just loosing it, causing damage to the front fender and running board. please get your setup fixed properly before your luck runs out !