Psychophanta: Official CapCom guidelines? I don't think there were any. lol.
The arcade machine was delivered about 3 months before its release (it had the II in the Jap title, a dip switch changed the title to Mercs - it's really Commando II). We digitized the gfx and re-did the maps slightly to fit the memory requirements of ALL the computer versions, CapCom did not give us access to the original graphics or program code/data. It all had to be reversed - this meant playing the arcade game a lot.
All the home computer versions (Amiga, ST, C64, Spectrum, etc) have an extra level that I created from the end of one of the official levels (the Train section). I don't think they noticed though. lol. One other thing was that the computer versions only had 2 characters, but the Arcade had three. I reversed 2 of the bitplanes on the Amiga version to get 4 sets of 4 colours - 2 for baddies, 2 for goodies - so there was not enough for the 3rd player (they all share the same gfx for the legs!).
I did meet the top people at CapCom though - they came over to visit USGold (Birmingham) then they visited Tiertex (Manchester) to see how we did things over here, everyone had to wear suits that day!
Konami did have a UK office back then - it was in a house near Bristol. I took SuperHero there to show them before Psygnosis bought the licence rights for the Amiga version.
nco2k: I didn't do the Genesis version of Mercs, they had access to the original gfx and code. The flame thrower in my versions (imho) was much better than the arcade/genesis versions - you could get powerup to make it stretch the whole screen. Great weapon.
byo: Do you mean in Cabal when they run up the screen - yeah it does look pretty funny. lol.