Do not worry about the apparent smallness of the stylus cantilever on the Dual cartridge, It will work just fine. I have 2 78 RPM cartridges. One is a Shure V-15IV with a VN4G 2 mil stylus on it. It looks just like the V15IV LP stylus, except the diamond is bigger. I also have a Shure M44 cartridge with a 3 mil Generic Shure stylus on it. It also looks exactly like the Shure N44-7 LP stylus except the diamond is bigger. You don't want to use those old fashioned needles with the screw in styli. You want to use cartridges and styli with higher compliance. A 78 RPM cart that tracks at 2-4 grams will work just fine, and will preserve your 78's. You will have to determine the correct ID of your Dual cart. It may be a Shure, or it may be an Ortofon, or it may be something else. You may have to use pictures to match it. A number of companies made carts for Dual.
You will not understand about preservation of records until you come upon a truly pristine 78. Most 78's are not in great shape, particularly the popular music that got played to death. Really clean 78's are rare as hen's teeth. I sent Phil a transfer of a truly pristine 78 that I got from my father's collection. Dad didn't play it because he didn't like it. I loved it. Pristine 78's are almost as good as playing the master disc. They are really quiet, and they have an impact and solidity that have to be heard to be believed. You will NOT want to use an old fashioned low compliance pickup that tracks at more than 10 grams grams on them, because you will not want to risk losing the peaks and the high frequencies. A good mono cart, like a GE RPX or VR II will sound good, but my M.O. has always been to use a modern high compliance pickup and the correct EQ with a little high frequency boost to get back the edge and the vocal sibilants. Keeps the records clean and quiet.
There are a VERY small number of post 1955 RIAA equalized 78's and a few that were pressed in vinyl. I have a half-dozen post 1955's, which have a REAL high end, and one album of vinyl 78's. The vinyl 78's are remarkably quiet.
A piece of unsolicited advice... Don't try to read the record label while it's spinning. You'll just get really dizzy.
And good luck from the old guy who watches the records go round and round and round and round and round.....