Thanks for all the suggestions! Many agreed that I would need to fabricate
the correct tool and offered clever instructions as to how.

I came up with a different solution, though: I inserted a 3" long brass
pipe between the block and the flexible hose. It's long enough to clear
the hole in the tin, hence can be grabbed and tightened. And since it
sticks out, it was easy to attach the hose. Slip a sparkplug seal over the
pipe to close the hole in the tin. Wahla. 

Sami