deff center mount them. your gunnna be in the park most of the time anyway so you will still have good snappy turns on the groomers. so i would deffinetly center mount them and get the 178 because you dont want them to be to small so get the 178 tell be perfect
Yes the chronic will feel short because of the rocker in the tip and tail. The 178 running length is actually 144. You can check it out on the line website.On larger jumps 20ft+ you will proably notice some washing out. If your on the rails most I say keep with the chronic. Maybe if your really worried jump up a size as the 185 running length is 151.
If your really into the jump sence and going big maybe somthing like the AR7 or Scott jib isnt a bad idea. Stay away from the suspects.
It does sound a little suspicous that he's recommending high end park skis, but if thats what your level is maybe go up to the next level of skis.