I replaced all of mine with stainless steel ones including the vacuum pipe a couple of months a go. With engine in place and I did not remove the windshield. The job wasn’t
that bad, just take your time because it’s a little tight, I have large hands.
I did take the dash top off for ease of access. Removed wiper motor and arm (don’t loose the clip) but left internal wiper rack in place. This way you can swing the wiper rack over and give you more room to install/maneuver the pipes. Also now is the time to replace the windshield washer hose. Mine were old and brittle. Also before removing old upper pipes, note the routing of the pipes through/around the heater control cable.
The key to an easy installation is to first maneuver the lower pipe (right to left) into the center square hole, then under the control cables, (then up and to the left) towards the heater box. This gives you enough room to then drop the right end of the pipe down, under, and then through the center bulk head support.
Before pop riveting the pipe in place, I ran some safety wire through the pipe, which allowed me to pull the pipe tight against the firewall, then pop rivet them in place one
at a time. I was able to pop rivet all pipes with engine in-situ using an old POP Rivetool gun Model K110.–
1969 SII OTS