351W require's different header's although there is a possibility that those shorty's you have now just may work.... you'd have to try, but it will be tight. The header's will bolt right on, but the problem is whether or not they will clear the steering shaft and they may be angled too much toward's the block as the 351 is wider and taller. To be honest with you I don't think they will fit. BBK, MAC, Hooker etc. etc. all make long tube and shorty header's for the 351W swap. As for your H Pipe, it may work with the shorty headers... the header's will be in a slightly different position but it shoudn't be too bad.... you'll just have to try it. The Cat Back set up will work just fine otherwise.
yeah, its between the 200 cc intake runner ones or the 215's, I honestly think the 215's are too large. Check them out, I think the 200cc intake runner tops out at 276 (or more) at .700 and exhaust was 193 at .500