Thank you, Mirko for your answer.
The problem does not lie in the power of the bulb ( I know of 65 mm diameter 250 W E27 bulb) but the size of the Opaline outer glass.
These enlarger have big condenser and if you want even lighting on the baseboard they require as big a bulb as possible.
Durst used 100 mm diameter bulbs when designing these beasts, and these bulbs where common then. Now they are long gone !
This is why I asked if someone can secure a bulb in the 250 ~ 300 W range but with as big a bulb as possible to go above the standard 65 mm diameter size.