Thanks Doug!
My primary references with regard to Panzer IV are mentioned in this topic:
Further- I often use a book written by Kaloyan Matev-“The Armoured Forces of the Bulgarian Army 1936-45: Operations, Vehicles, Equipment, Organisation, Camouflage & Markings”, with plenty of HQ pictures of Bulgarian Maybachs, info on delivery batches, Fahrgestellnummer and vehicle distribution.
HTH,
Cheers,
Angel