Adrian
The Axis History Forum has some good stuff on this. In essence the Flak 18 and Flak 36 barrels were interchangeable:
8.8 cm Flak 18 (First of type)
8.8 cm Flak 36 (Redesign of the Flak 18 with minor ghanges in carriage and barrel made in three sections instead of one)
8.8 cm Flak 37 (Improvements in the data transmision system and a new barrel in two sections)
8.8 cm Flak 37/41 (Flak 41 barrel on the Flak 37 carriage)
8.8 cm Flak 36/43 (Flak 41 barrel on the Flak 36 carriage)
8.8 cm Flak 39/41 (Flak 41 barrel on the 10.5 cm Flak 39 carriage)
8.8 cm Flak 41 (New design by Rheinmetall, the gun was mounted in a turntable, with great improvements in ballistics, a powered loading mechanism and a three sections barrel in the first guns produced and a two sections in the latest)
8.8 cm Gerät 42 (Krupp design for the same specification of the Flak 41, not accepted for service)
As to Flak 36 with the DAK, I've found reference to at least one battalion equipped with it by early 1942 and it appears that the later Flak 41 got into Tunisia in early 1943. It wasn't very popular and there are references to crews abandoning them in favour of preserving their Flak 18 and 36.
This is quite a good summary but there's lot of stuff around.
http://www.achtungpanzer.com/88mm-flak- ... kanone.htm
All the best
Stephen
http://www.achtungpanzer.com/88mm-flak- ... kanone.htm