From memory it's been a while since I've stripped an 600's corbs off: -
Pic 1, Large black T union in the centre is the vacuum, which should have a elbow with a filter built in and face back towards the airbox, it's possibly still in the hose. The 2 smaller black T unions either side should be pointing straight down (6 O'clock) to the float bowls, these are fuel return lines, brown T union is fuel feed and should be point straight up (12 O'clock)but slightly forward, Pics 2-3 are the heater lines and they look correct.
Before you put them back on, check all the water heater elbows are clear, as this is where they block
Pic 1, Large black T union in the centre is the vacuum, which should have a elbow with a filter built in and face back towards the airbox, it's possibly still in the hose. The 2 smaller black T unions either side should be pointing straight down (6 O'clock) to the float bowls, these are fuel return lines, brown T union is fuel feed and should be point straight up (12 O'clock)but slightly forward, Pics 2-3 are the heater lines and they look correct.
Before you put them back on, check all the water heater elbows are clear, as this is where they block
Later