1990 360 engine, trying to retrofit it to use a mechanical fuel pump.

woof. i'd say the water ingress is from there not being a carb on it... rarely do you get intake runners that funkalicious from a bad headgasket or cracked head/seat area.

we talked about this previously...

https://www.forabodiesonly.com/mopar/threads/mechanical-fuel-pump-on-a-roller-cammed-360.566549/
i'll echo what killer and 72 said: check what you've got cookin' first and if you do need the adapter hughes is the place to get it. for better or for worse.