Screw an all-thread nipple into the manifold, and put a "T" fitting onto that. Then screw both sending units into the T, one on each side. Problem solved! You can also use a nipple and a coupling at the thermostat housing to adapt one sender there- - - -once the engine warms up, there won't be enough temp drop across the thermostat to matter!
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!