I have to agree with rhino. 1/4-28 has been used many times in the past and is fine. however I too believe you will find a metric that will fall in between 10-32 and 1/4-28. what you realy NEED to do is find out what size your holes are now. this will determin if you can even use the metric size or are you oversize for them too. If yes then it will be the 1/4-28 anyway.
one last note ,ware the rivets came out are your holes round and just oversize or are they egg shaped at all from the rivet?? if they are egged out they will need to be drilled till they are round before you measure for thread size. As mentioned above if they are too big they will need to be filled and re drilled,,,,, but a 1/4-28 is fairly large so I doubt you are over its size for tapping .
good luck ,,, welcome to the board. keep posting and reading and your kit will end up great