The picture below shows how the much space there is (I used a couple of bits of scrap pipe):
Some people run the brake pipe between the fuel pipes. Some attach to the box section of the chassis rather than the lowered part of the floor. I adopted to start with the fuel pipes then see how it looks later!
Front end:
On the suggestion of another builder (Inge Jonsson) I made the lengths of the 2 pipes different. This makes connecting the flexible hoses simpler later as the clamps are offset. I started the bend 170mm from the end of the inside pipe and 190mm on the outside pipe.
I also took the tip from Inge about mounting the pipes slightly away from the panel. You can do this as you are attaching to a panel rather than into the chassis box section. Inge used a 10mm length x 10mm dia. piece of brass pipe with a M4 bolt/locknut. As a temporary measure I used one of those plastic blocks used to fix the corner of bookcases. Fixing the pipe 10mm away from the panel also has the advantage that you can put a simple right angle bend without having to put a swan neck in.
The inner pipe has to be min 25mm from the inside edge of the tunnel. This means there isn't enough space to the master clutch cylinder for the 2nd pipe to be connected by jointly riveted P clips (like in the picture above). The approach most builders seem to take is to make the pipes converge towards the front with separately riveted P clips then let them diverge after the pipes are past the clutch cylinder.
Mid-section:
The inner pipe just needs a simple bend in the middle.
The holes for the rivets go are through the floor of the chassis rather than into the box section so you have access to the other side. As a consequence I could temporarily attach the P clips using M4 bolts trough the 4.1mm holes (the only ones to hand were courtesy of Ikea bookcase connectors). When I come to do the final rivets I'll probably rivet the front section from the inside so the flat part of the rivet will be on the inside and so the carpets will be flat.
Rear:
The 1st bend was okay but I got the 2nd bend slighly in the wrong place so the pipe went along the centre of the chassis section rather than the edge. I might try to straighten out the bends to move it over slightly. As you are attaching to box section, rivets must be used so I can't use the same trick of a space like I used at the front. Instead I bent the pipe down so it was away from the chassis providing clearance for the flexible hoses and clamps.
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