Thanks for all the advice.

I've been waffling over what to do with this frame ever since I got it, and I thought I had arrived at a final solution with removing this stop and adding the clamp-on stops to accommodate the Shimano 600 group.

Then I got a price from a local frame builder to move the rear stop to the top of the chainstay and add another one for the FD to the down tube - $50 - so that's what I'm going to do. Much cleaner look.

Thanks again.