Salve Jorge,

As I have always played with Durst enlargers, from 6x6cm to 5x7', soon I learned that one can't fool around with optical geometry (as an engineer, I suppose you know what I mean). With Durst bigger enlargers one needs to check both condensors, their distance from lens, bulb size and position on XYZ space, magnification and, if one really wants to be precise, the filament position inside de bulb. Once it's all set, light distribution is so even as it can be.
Regarding to Opemus III, I could suggest you try both ways: 60mm lens and 1- turning the head for floor projection or 2- using a wood block 10/15cm high under the column, so to allow 30x40cm projection on the board.
BTW, as I'm also brazilian, feel free to e-mail if you want. Certo?

Cesar Barreto