Been there, done it. I replaced all fuel lines from the pipes which come up from driver side firewall till the end where they go back to the charcoal filter and then are connected to a pipe which goes back into the tank.
Check all connections, replace all BMW one-way-hose clamps, place an order to Autohaus Arizona for the fuel hoses (in my case 2 sizes /diameter) and you can spend a nice weekend in the engine room.
Not that easy on a 750, probably more difficult on a 850, as there will be less space even.
On Bimmerboard E32 there is an instruction for the 750, maybe that hekps a bit
http://www.bimmerboard.com/members/l...re%20Hoses.pdf