Rick, the trick to figure out what notes are used in the keys of F and C, and then double them up to the 36 total strings on the harp. Thus, you will have 18 pairs of strings to work with, with some notes like C, F, B etc which will double for some chord bars in both keys. Lay it out on a piece of paper and it will soon be clear to you. Remember that you must also cut the chord bar felts to reflect the two free strings for each note, so take a look at the chord bars that have one or two notes in common with another chord (think 7ths) before you lay out your strings, and cut your felts. Other than volume and a larger area to lay in your pinch for solos, I still go chromatic, unless I was solo and singing. But relatively modest players can still sound great, which is why in WVa they are called "Cheater Harps".

This can also be done with any root chord and its sub-dominant, like A and D, G and C, etc. Good Luck!