I would love to put some down tube shifters on it, but have always been unsure if I could mount them since it does not have the braze-on mounts. ( it does however, have a little triangle 'knock' on the underside of the frame where the chrome cable mount is on the downtube ) Any advice on what to look for in these?

I definitely plan on keeping it for quite a while. Seems like a solidly built bike with many years of service left. I have already put a little over 200 miles on it and it has done great.