The 27 was replaced in the early 1980s by the models 26 and 28. Those have gone through a lot of evolution over the years and are kinda hard to find in the US.
The 27 was of course an old-skool design with leather piston seal, no safety, and ball-sear trigger. The 26/28 are of similar design to the model 34; plastic seals, safety, new modular trigger designs.
The current model 24 (or "two forty" as now named) is easier to find, but a somewhat smaller and less powerful gun. More like the classic model 25 than the 27.
Hopefully others will chime in, newer Dianas are not my thing!