Klavs (@klavs1972), no, you are not wrong, but not correct either – to the best of my knowledge they both had the small stub-exhausts, and even some B models did have them (page 155 in “German Eagles in Spanish Skies shows 109B 6O44 with exhauststubs) and in “Die 109” from 2008 there is a 109 C-2 on page 31 with stubs too).
The hatches for the wing-mounted MG were also a feature of the C, as they had the enginemounted MG deleted, keeping the two in the cowl and had two installed in the wings. I will have to double-check if there is a difference to how they look, but some C-1’s were re-engined and were referred to as D-1’s after that.
In the german-language “Die 109” from Motor Buch Verlag, there are pictures of 109C with and without, and even some with mid-war school 109C’s with E-like exhaustshrouds.
I will get back to the armchair and Coffee and check some of the LiF magazines by “Start”, and if something conclusive turns up I will let you know. Hope this helps – no matter what you are well off by calling N+8 a D-1, so lets see more of this great choice my friend!