Different than the pictures on the website my R275 came with a tapered headtub and flat mount brake. Lynskeys site still has pics of the R265. Their camera must have run out of film.....
I like the look of the tapered headtube better than straight for sure. Frankly I cannot see much if any difference from the R260 and the R275.
Headset just buy inset 42/52 as recommended for the R260. The bottom piece you will just need the bearing and race (no cup) and for the top just a bearing and top cap / race. Cane Creek makes 40’s and 110’s that fit the Lynskeys.