well, i used the mount from that guy barry and it worked out great.
yes, the mount is necessary because it off-sets the engine to the left to allow the chain to clear the rear tire. there are other mounts out there and i really don't know much about them other than i heard that the livefastmotors mount is ugly. there is also a mount that boygofast sells and it is similar to barry's mount, but it clamps to the frame so you don't have to drill holes in the frame. BUT, in my opinion, the clamps look out of place, and they don't make the mount as clean looking as barry's mount. on top of that, i have no idea how well the boygofast mount is welded. I can tell you that barry's mount is welded very well and that he uses high quality, very thick steel and pipes to make the mount. I have no idea about what kind of materials the boygofast or the livefastmotors mounts are made out of, and i have no idea how well/poorly they are welded together. this is just opinion from what i have heard, i have never personally seen either one of these mounts.
in my opinion, barry's mount is the way to go, but a lot of people will shy away frm it because you have to drill holes in the frame.
the adapter you show is just a different way to mount the sprocket to the rim. it bolts to the hub (which requires drilling a hole in your hub) but it is not necessary to use that adapter. the stock rag joint connector will work fine to mount the sprocket to the wheel. the only thing is that with the occ rear hub, you will have to elongate the bolt holes in the sprocket so the bolts clear the hub where the spokes go through it. I elongated the holes in my sprocket with a drill and a drill bit. it worked great and it was pretty easy to do. that adapter does not replace the kit sprocket, it just allows you to bolt the kit sprocket to it. you bolt the adapter to the hub, and then bolt the kit sprocket to the adapter. i have a 41 tooth sprocket on mine and it works good. I have plenty of chain clearance where the chain goes past the frame. if you go to a smaller rear sprocket, the chain may rub on the frames swingarm.
no, you have to use the chain that comes with your engine kit. a bmx chain will go around the rear sprocket and fit the teeth, but it will not go around and fit the teeth the engine sprocket.
you can use the stock caliper rear brake that comes on your bike, but you will have to modify it a little. you will have to cut off 1/4 of the left brake pad so the chain can clear it, and you will have to raise the left brake caliper up (or bend it) for chain clearance. i raised mine with spacers and slightly bent it up.
i am using the stock brake (rear only) and it works good...not GREAT, but good enough to stop the bike.
if you buy barry's exhaust pipe be ready to shell out $75.00 plus shipping for it, and be ready for it to be VERY loud. these pipes do not have a muffler, they are just straight pipes and they are painted flat black. i know that he says that you can send him a muffler and he will build you a pipe with the muffler on it, but that is still expensive.
I built my own pipe by using a chrome extended pipe ($34.00). I had to cut the flange off where it bolts to the engine and weld on 4 inch extension so the pipe would wrap around the cranks. i also modified the muffler to make it flow better (and it is slightly louder than a stock muffler).if you buy the extended pipe, it will not be long enough to clear the cranks so you have to extend it before the bend. i bought my extended pipe from boygofast in e-bay.
things you need to know:
be prepared to make some modifications. think about making your own chain tensioner because the one that comes with the engine kit is junk. (not to mention that it's UGLY). you will have to get some more links of chain because the kit supplied chain will not be long enough. you will have to shorten the clutch cable and the throttle cable because they will be WAY too long on this bike. unless you want them to be dragling down almost to the ground.
you may have to grind down the inside of the left crank because it may hit the engine side cover. (this happened on my bike) you may have to remove the left peddle and put a spacer (a thick washer) on it, and then put the peddle back on, the peddle threads extend into the crank and out the other side, and will make contact with the engine side cover.
if you use barry's mount, be sure to follow his instructions because it is a 3 peice mount, and it only works RIGHT of you put the peices on EXACTLY how he says in the instructions. you may want to put some rubber in between the peices fo the mount and the frame to help with vibration, I used some silicone heater hose (for semi trucks) and it helped. i ran it fisrt with no rubber in between the mount and the frame, and it vibrated VERY bad. the rubber helped but i still have a vibration at top speed when the engine is at it's peak rpms.
you will have to trim the left side of your rear fender for chain clearance.
i suggest getting a set of chain adjusters that go on the rear axle (barry sent me a pair when i bought his mount, and he still may be sending them to people who buy his mount). the chain adjusters make it simple to adjust chain tension.
there are a lot of other things that i did with my occ build just because i wanted to customize it more and i wanted it to be a unique build. I made a lot of parts for mine, and i hid 80% of the wiring because that's just the way i am. i like nice, clean un-cluttered, and custom looking bikes.