You'll need a pump shoe and an impeller. Basically your only two choices for the pump shoe are Jet Dynamics and RRP. The RRP is a little nicer, a little more expensive. To be honest, in my opinion they both kinda suck, but they work. I used an RRP. It fit with minimal grinding/trimming. I've heard that the Jet Dynamics shoes require a lot of fitting but I don't know.
For the impeller, the skat trak C75 swirl is basically the only choice. As previously discussed in this thread, you'll probably be somewhere in the 6/12-7/14 neighborhood. I'm really guessing about the pitch so take it with a grain of salt.
For the pump itself, probably the cheapest way is to get a complete setup from a couch on ebay. They sell pretty cheap on there. Usually you end up with some stuff you won't use (couch shaft, couch impeller, and big cast aluminum pump tunnel thing). 155 reduction nozzles are bigger than 144, not interchangeable, also 155 steer nozzles are bigger. I'm not sure about the trim rings, so I'm not sure if your xmetal trim system will work. You can also get pump parts from JetManiac, you'll probably spend a little more, but you'll be sure they're good parts vs the ebay gamble.
The shaft really should be a little longer as Sasquachcrap pointed out. I got away with a stock length superjet shaft on mine by mounting the motor as far back as possible, spacing the coupler a little, pushing the midshaft back in the housing a little, and accepting a little less than full engagement on the splines. It's about ~10mm to make up. If you do the "full pump assembly from ebay" route on the pump, you'll have a long couch shaft that can be used as a core to be shortened for a custom shaft it you want to go that way.
Be a little careful with the reduction nozzle. Some of the couches came with upward angled nozzles, some came straight, some came with trim rings and some didn't. My Chan porpoised horribly with an upward angled nozzle, but was fine with a straight one.
Another thing to look out for is that the long bolts that hold the pump together are bigger in diameter on the 155 pumps, and all but a B2 pump the bolts go into the big cast pump shoe thing rather than threading into the wear ring flange so they can't be used in your setup on your chan. They're too long and there's nothing thread them into. The easy route is to either get a B2 wear ring and bolts (they use a threaded wear ring and shorter bolts), or use short bolts and nuts on the individual joints rather than the single set of long bolts.
You'll also need a seal.
The hub spacer sleeve dealio that you have on your 144 pump has been modified to fit on 155 pumps by a few people, search around and you can find info, might not be a bad idea.
Jetmaniac has the shoe, impellers, seal, and the pump parts if you choose to go that route. Highly recommend.
I think the whole assembly from Sasquatcrap looks pretty good too, but have no experience.
