A lot of old threads on center tunnel rust/cleaning, but I'm wondering if there would be any problems with the plastic fuel lines if Ospho was used in the tunnel??

very good question. i used metal ready (similar to ospho) during my first ground up restoration.

about 3 years later, i pulled the plastic lines and replaced them with stainless steel lines.
as far as i could tell, the plastic lines were in good shape and showed no signs of deterioration.

not very scientific, i know ...
Andy

If you are going to the trouble of using Ospho in the center tunnel, and painting the inside with something like Zero Rust, go ahead and finish the job right by replacing the plastic fuel lines with metal while you are there... because you will
have to replace them...it is just a matter of when -
Buy them from Chris @ CFR-
Just my .02...

Best -
Thom

Ospho is osphoric acid. Acid eats things and makes them thinner. Not 100% sure what they would do to the long chain polymers in the fuel line, but I think it is a safe bet they won't be better than they are. Acids will probably break the bonds on some of the long chains (to some depth) and the broken chains are less strong. My gut is short term - probably nothing, longer term- the lines will be more brittle and more likely to fail.

If you apply the ospho and leave it, the evaporated residue is acidic. You might want a thin baking soda wash in there to neutralize the acid so it won't keep eating the polymers, and a wash to remove the baking soda. Then apply a coating of cavity wax.