He is talking about an 750 "il" here, there is NO way the 5 series will have near the same amount of room as the 7.
As a BMW dealership mechanic, I would advise against such a purchase, at 130K miles, the engine is reaching (if not already passed) the end of it's good service life (poorly serviced cars are WAY lower than that...) before a rebuilt.
Just think about having to buy 12 BMW pistons, 12 rods, 16 valves and so forth, plus the time consuming task (if you do it yourself) or the money involved (if you have it done) to remove this complex piece of an engine from the car, open it, measure all those parts, reassemble, put back in...
It's not worth it, sure you can get a 12 cyl. for $500 at the junkyard but, odds are that it will be in worst condition than yours...
Like I say to everyone who asks, people come in to see us all the time with a big grin on there face, all happy about there new toy they just bought from a private garage, looking to get it inspected to know what it NEEDS and (no joke here) many of them start crying when we tell them they have about 10 to 12 grands (which is about what they paid for the car) to put in the car, to bring it back to it's original glory.
They are very comfy, always broken cars with a lot of bells & whistles that can go wrong and are pretty expensive to fix.