Hello,
I think either can be fitted. 25D dizzys have long clips holding the cap on (around 3") and 45D have short ones (about 1 1/2") the points are different too. On a 25D the end of the spring is held by a nut, on a 45D its kinda loose and fitted with a little plastic shim.
And finally, 25D has a little spade connector for the low tension wire, on the 45D it comes via little rubber grommet through the Dizzy housing.
This website is pretty good for bits and might help with identifications.
nothing stamped on mine helpfully enough - have got electronic ignition on Bessie - old system so a bit rickety at times but when it works it works well