I've used this design twice now, once for my 4805 and then again with my HC1500.
I'm impressed with the ingenuity of MonkyMan's mount.
I did things slightly different from the original design, however. I used a piece of wood for the plate the second time around as plexy just felt too wobbly for my tastes. In fact, in some of the earlier pictures, you can see the plexy bowing under the weight of the pj. (plus, the wood for my new plate was free from the scrap I had laying around)
Second, rather then trying to find long M4 bolts (which was just too hard and special order defeated the purpose of a cheap and easy mount) I used the longest M4 bolts I I could find at Lowes, 30mm to bolt the plate to the pj, using rubber washers to cut vibration transmission. I used 3in 10-24 bolts screwed through the bottom of the plate to attach it to the lower bracket. I used wingnuts so I could adjust the positioning once I had it up there.
My first design, I did it the other way around and ended up needing to spin the whole projector to get the thing down. Now I can just unscrew the four wingnuts and drop it off.
I didn't, however, think of using compression springs, just gravity. That was a brilliant notion on whoever thought of that's part. I'm going to add them to my design.
I might even sand and paint the plate while I have it town. For now, it just looks like a scrap of wood.
I'm not too worried about aesthetics though, I mean, it's 6 inches from the ceiling, you can barely see the mount as it is.