The Hispano engine and indeed, all prewar engines/most early war engines, did not have a War Emergency Power rating.
Some Hispanos were rated at 830-835hp for take-off (they had to be throttled back) and 860hp at altitude (3250-3300 meters). I wouldn't worry about 838 vs 830hp on a licence built engine.
The Hispanos ran on 87 octane fuel and the chances of the users of the B-135 (or any other users of Czech aircraft) getting any better fuel to try overboosting with are pretty slim.