jdm h22 after swap

i recieved an exhast manifold as well as a downpipe with my h22a swap, come to find out that the dowpipe doesnt mount up right to the random technology cat, my question is whether i need to change over completely to a h22a exhaust including the cat or could i jus relpce the cat.
also could it a problem with the jdm header?, would a new header mount up to the R/T cat?

anyone know?

replace the cat. Just make sure you get the right matching flanges and size cat.