Regarding the fuel lines, there are 2 metal pipes (delivery and return), which I'd only replace if they were damaged or rusty, plus 7 rubber hose sections, which I advocate replacing. 35 year old rubber fuel lines tend to be brittle and cracked, basically not very trustworthy. There are 3 hose sections at the tank/fuel pump, and 4 in the engine compartment. You can probably do all of them for around $80-100.
The hoses are similar for all models, but there are some differences in end fittings here and there, so order from someone who really knows their stuff, like Ray Paul at SL Classics.
George Davis
'69 280 SL Euro manual