Yeah the height of the shoreline will be ~.062" if you use .058 for the "lug". The difference being the clearance between the two tubes, which will hopefully be filled with braze. 60 thou is OK for brazing practice, but looks terrible on a bike to ride and will probably result in shorter fatigue endurance. Large sudden changes in section thickness cause stress-risers, where fatigue cracks will start. So your lug should be thin compared to the tube wall. 40 thou would be OK but 30 would be better.

If you are lacking a lathe, you'll want to file the "lug" down either before or after brazing. I prefer before, because the brazing will go a little quicker, and there's no chance of accidentally thinning the tube that way. But there might be practical reasons to file it after. Or a combo, some before and some after.

If you just want to see how much penetration you got, on a testing sample, leaving it full-thick is OK. But then when you braze a real lug you may be surprised by how much faster the lug heats up.