There was somewhat of a trend in the 1970's for painting the inside of drums for extra resonance, and some manufacturers did it too, but I'm not sure if Ludwig ever did it. Could be the previous owner modified the floor because he wanted particular resonance from that drum?

Hi.

Ludwig did some mix/match shells during that era. By that time, Ludwig was no longer tucking the wrap into the seams of the 3-ply shells, so it wouldn't have been out of the question for them to use whatever shells they happen to have on hand -whether the interiors were painted or not. There's really no rhyme or reason to it. Some of the shells that had interior blemishes or discolorations usually got the paint -and then subsequently a scheme was thought up to cover up the cover-up, stating that the paint helped resonance, etc.

The kit looks like a good candidate for restoration and they are definitely matched badge numbers, so that's a good thing.

Parts are available online.

Ludwig started using a granitone interior paint in the early 70's. Don't know why or how long it lasted. Looks like some drums were clear and some were painted. That is common of your set. I have a 1973-ish jazzette and the drums all have the granitone paint.