Roger, i just (OK, 2 mos ago,) changed the impeller on Journey On's 150. It was an easy job. I do have the following comments.
1. I got the parts from :
Honda Outboard Parts. Saves a little, but more important, they actually look up the correct part for your serial number, if you order by phone. Good service. Get the kit: impeller, gaskets, housing, etc. $45.
2. I also got the Honda service manual. Lots of drawings to show where and which way the parts go. Used it liberally. Or take lots of photos. Got mine through Helm, order by phone.
3. The gearcase slides down when the last bolt is out, and it isn't light. Be prepared. I put the motor straight up. Dealer has a hydraulic lift, but I (and Judy) held it by hand.
4. Rest is straightforward. The hardest parts, and they aren't that hard is to get the !@# impeller in the housing and fit the gearcase back up. Need two people for the gearcase, fitting the driveshaft and the shift lever.
Worked well, saved a 200 mi round trip to the dealer, etc. 300 hrs, and the impeller still had the mold marks.
Boris