For what it's worth, I tried making a longhood heater duct. After a lot of prototypes, I got it to fit nicely.
I made it out of ABS and it just did not work. The proximity to the cylinder head and heat cycles warped it, and made it soft enough while driving that the bolts became lose and backed out. I did not try PAHT, which might have faired better, but got tired of the effort.
I also made a oil filler after spilling oil all over using my old funnel. Having it secured to the filler pipe is so much better.
