smack in the middle of this tome I'm reading, I find the following:

..the downstream tip of the Ile de la Cite, spang in the center of the Pont-Neuf.

both spang and smack would seem to mean precisely or directly in these contexts; although I suppose smack-dab would suggest more-precisely. :)

I've often heard smack used in this sense, spang springs entire new upon me.

spang in the center of ~ 2 gh
spang in the middle of ~ 71 gh
smack in the middle of ~ 136,000 gh
smack-dab in the middle of ~ 86,500 gh