I struck gold in my search for good documentation on the Bf-110D, E, and F series.
This site has the original German manuals for installing ventral cannon packs, and the various ETC bomb racks.
http://www.deutscheluftwaffe.de/arch...cmitt%20AG.htm
Absolutely comprehensive technical report for captured unnamed Bf-110 variant, but very likely the D-2, E-2, or F-2 variant since it included a rescue raft compartment and ETC 500 bomb racks. The only weakness in the report - other than not describing the exact variant - is that all armor appears to have been removed from the plane, so no information exists.
http://www.deutscheluftwaffe.de/arch...20Me%20110.pdf
Installing ETC bomb racks on BF-110E:
http://www.deutscheluftwaffe.de/arch...%20Wartung.pdf
R-1 ventral cannon installation for F & G:
http://www.deutscheluftwaffe.de/arch...eiheft%202.pdf
Manual for installation of drop tanks and "dackelbauch" tank for D model:
http://www.deutscheluftwaffe.de/arch...atzanlagen.pdf
Installation of ETC bomb racks on E model:
http://www.deutscheluftwaffe.de/arch...%20Wartung.pdf
Plenty of good pictures here - with Russian captions:
http://aviadejavu.ru/Site/Crafts/Craft20512.htm