Installed the plastic sight plugs that came with the new Holley that I just bought so that I could adjust the fuel levels. Put both plugs in finger tight and made all the adjustments. When I was done I went to put the brass plugs back in and found that one of the plastic plugs had broken off with the threaded part still in the carb. The plug had not been damaged in any way prior to being installed. The outer piece just broke off and fell onto the manifold. I was lucky in that I was able to get the threaded piece out but I thought man this could ruin your day if you had to remove the fuel bowl. Anyway just thought I'd mention it and maybe save someone else a headache.
Same thing happened to me but I was using Quick Fuel Technology plastic sight plugs. I wouldn't doubt that the plugs are all made by one company.
Looooong time ago, holley had a sight glass(lexan) that attached at the upper and lower float bowl bolt holes....havent seen them in a while....