i couldnt see the prob with a sling , as long as you keep the motor level when marking out the holes if needed. make sure its secure before lifting. they use slings for large motors so why not outboards

 I've had another look and I'm not going to use a sling. Too much plastic around it and too much risk of damage.

 PS: Holes are already there. Just want to do a height adjustment.

Im not sure on the news mercs but lce raised and lowered big motors just using the jockeywheel and afew blocks of wood

 Just loosen bottom bolts 

 Timber under the skeg and use the jocky wheel? THe bottom holes on the Merc 150 are slotted anyway so just need to be loosened not removed.

www.suzukioutboardforum.com/suzuki-outboard-parts-forum/6264-how-set-engine-height-select-right-prop.html

How to lift outboard engine height at home using your boat trailer.

We have used this method to lift 4 cyl motors and even some smaller V6's. (The bigger motors are best done using some form of lifting device. A block and tackle attached to the motor lifting points is one way.)

Tools and supplies:
- You will need yourself plus 2 people to help. Some strength is required so choose accordingly!
- Tools- wrench or sockets of correct size for nuts on transom bolts. Plus a paint scraper to scrape old Sika off.
- Supplies - sealant such as 4200 or Sika 291 to seal the bolts where they penetrate the transom. Some alcohol based solvent to clean up excess Sika. We use methylated spirits.

1. Put boat/trailer on a flat piece of ground, and chock the wheels so trailer can't move. Disconnect from tow vehicle. Trim the motor down so it is vertical.
2. Place a block of heavy wood under the outboard skeg so it is an inch or so below the skeg. You might need to use some bricks etc to get it to that height, just make sure they are very stable as they will need to take the weight of the outboard and be stable.
3. Wind the jockey wheel up - this will lower the stern of the boat. Wind until the skeg is sitting firmly on the block of wood you put there in step 2. It should be clearly taking the weight of the motor. The skeg is easily strong enough to take the motors full weight in this position.
4. Loosen the bolts holding the motor on. Some motors have a slot on the bottom bolts, if so, they just need to be loosened off so the motor can easily slide up or down. If not, all bolts have to be loosened right off and the nuts removed. 
5. At this point your helpers need to be on each side of the motor, holding it steady. They can now carefully tilt the motor slightly back so it comes off the bolts. 
6. While they balance the motor, you go back to the front of the trailer and wind the jockey wheel up some more, and your helpers tell you when it is enough so the bolts line up with the correct holes in the motor bracket that you want to use. 
7. Go back around to the motor and clean the old Sika from around the bolts, use the scraper to clean it up, and then apply some fresh Sika to the bolts and adjacent area so it will all seal up properly again.
8. Slide the motor back onto the bolts and put the nuts on and tighten up. Clean up excess Sika as required.
9. Wind the jockey wheel back down so the bolts are once again taking to weight o ft he motor, and check that it is all good and hasn't moved. 

 Thanks Darren,

Makes perfect sense to me and should do the trick. Yes bottom bolts are slotted so they will keep the mottor from going too far. I was toying with using a bottle type car jack to lower it but this is just as good so I'll give it a go.