Highest quality? Either Ilfochrome print by someone who is really talented and probably very expensive, or find someone with a stash of inter-negative material and the skill to use it. Alternatively, a high resolution scan (minimum Nikon 8000/9000, but drum scan better) plus top notch post processing and pro-lab RA4 print.

If you haven't done this sort of work in the past, a 20 x 30 is not the place to start .