Yep, .003" should be fine, the deal is the bronze expands with heat, and since it is sitting on the guide bore hole in the head, it has no where to expand but on the ID. Here's the deal though, it often time is near impossible to find bronze reamers for the sizes we need and with anormal steel reamers they often times grab inside the guide, and as cheesy as it may sound, you often times need to use a drill bit as a reamer to get the right size, for example on a A series engine you need a 9/32" reamer and no one makes one for bronze, just steel, so I use a 9/32" drill bit for the first fitting and then a 7mm flex hone to put my finish on them. Bronze is a unique material to have to machine, it does not like cutting oils when being machined, so it has to machined dry.