of course some wiseguy always comes in with a different opinion...
i have a 1565cc renault R16 motor with twin weber DCOEs. i drilled a hole in each runner, tapped in a piece of brass tube, made a small plenum out of brass sheet, ran vac hose from the 4 runners to the plenum. one tube out to the MJ sees dead steady vacuum. the cam is stock, but my hunch is that no matter how wild your cam, i wouldnt think it would introduce enough pulsation to upset this arrangement (on account of the motor being, what?, 2litre?).
it may well be that a TPS is easier to fit, and a better solution for that reason, but my feeling is that MAP option is still completely viable. i bent and soldered the plenum, but you could just as easily glue the tubes into any small tin or plastic box eg an abs electronics hobby box for instance.
regards
alexander.