qiute right the hot cold is the wrong way round to fit the later heater means modifying the bulkhead prob is with the centre vent it can be got round buy using ducting and a couple of Y joints all readaly avalable from brakers yards and some duct tape
Havent a clue found one one in a pile of junk !! you could make one up useing some suitable plastic pipe and a mitre saw and block and glue it all together .But is it worth all the hastle?? its only the centre vent that is the problem .