Whoaw!! HandyAndy seems to have a circular metal ring that is attached to firewall which goes around the wiper motor, getting sealed up with a piece of innertube, whereas Greg Brown, you do not have such a ring per your pics. So unless you have such a metal ring, you will need to find another way to seal between the motor and firewall.
Craig
My '50 Chevy 3100 5 window, '62-235cu, 3:55 rear
My truck ....... Respect The Rust
If I'm not working on my truck, '65 m00stang or VW camper, I'm fishing with the wife or smoking Salmon.