No way is there anywhere near enough room for coil-in-cap on a Slant-6. Optimal parts selection is discussed in the HEI upgrade article, and as far as caps and rotors go, read and follow the suggestions in this long (but worthwhile) thread.
yikes, a lot of reading here. have seen a HEI made by a Mopar distributor that looks decent, have some follow up to do but is not a name brand: eBay (ebaydesc.com)