I've seen some internal honda engine cases and covers that had oversray on the insides. But in those cases, not all of the insides were black. I know some people who build high performance engines often use a coating on the inside of their engines to help with the oil returning to the oil pump faster but that coating is usally a dull red color not black. I think your engine just needs a real good soaking in a parts degreaser tank or maybe a nice steam cleaning.
Nicholson 500x (Project)
Nicholson 185s
Nicholson 110 (That takes an atc70 tank)
Ascott 500 head/350x (Project)
Homebuilt Racer Chromoly Suspension 110 (Ragin Runt)
PK Racing Suspension 70
A+ Inc Suspension 70
AWS Aluminum 90 frame
Hi Performance ATC Suspension frame rd350
Hi Performance ATC Suspension frame 90