I just got into Pentax 67 as well. First I got an old 6x7 body on the cheap, but after looking through the prism, I saw that I could not even focus with the 105/2,4 because it was horribly dim. The lens was yellow too - probably radioactive...
I have bought then the 67II body with metered prism, and this is much brighter, but the magnification is smaller, arrgh... I have the following question: has anybody compared the brightness of the plain non metered old and new Pentax 67 prism? Is the difference in brightness given by the focusing screen only, or is it also the old prism that eats away the light? I have bought a screen for Pentax 67II and I would like to fit it to my old one after removing the frame - apparently this can be done...