273/235 Gas/Octane Requirements

My oldest son (who lives in the Netherlands) will eventually be getting the 65 4 speed Barracuda I have. The motor that's in it - 273 2 barrel - has no oil pressure so I located a true 273/235 10 plus compression ratio motor which is in the process of being rebuilt. He asked about gas octane needed for this motor. He stated they have 95 and 98 octane there in the Netherlands but apparently might be measured differently there. He did say there is a higher octane (100) he saw in Germany but not available in the Netherlands. I don't know and he can't confirm but I suspect his 95 might be equivalent to our 87 and his 98 to our 91. I told him this motor with the 10 plus compression ration will need at least our 93 octane to be happy. Told him maybe an octane booster might have to be used or lower the compression of the motor or set up the timing differently or maybe use a warmed over 318 that would run good on his 98 octane. Thoughts?