[sww914]

There are 2 timing chains, one for each side, 2 cams. These are interference engines, many timing chain issues = bent valves. You can't successfully tear the cam timing area of a 911 engine apart and reassemble it without experience or books. This is not a small block Chevy or a Honda. There aren't any timing marks to line up, you must time the cams by measuring the amount of lift at the valves with a dial indicator, a special fixture, and a long set of instructions. You should buy Wayne Dempsey's book (he owns Pelican Parts) before your friend buys the car, and probably Bruce Anderson's book too. I recently bought a 2.7 that was "rebuilt" by a mechanic that didn't know Porsches, He ruined the cams, valves, pistons and cylinders, and stripped a couple of bolt holes in the case. I think that he might have been able to pull it off if he'd bought at least one of the books for about $20.00. Instead he ruined $1500.00 worth of parts (used). If it needs timing chains it might really need tensioners or a Carrera chain tensioner upgrade if this hasn't already been done, the parts for the upgrade are around $650.00.
You need more information than you will probably get anyone to type out here. In my opinion a 911 engine has more in common with an aircraft engine that it does with most automobile engines.
I would rather drop the engine for that job. It's possible to replace the chains in the car, but not by much. These engines are too easy to remove to make it worth it to deal with the frustration of limited access and poor visibility.
BTW, a 3.0 has a part number starting with 930 on the side of the case visible from under the car, 2.7's and smaller have a 901 part number.