OK , I was afraid of this, what you need is a screw extractor , the type which is square and has one "flute" on each corner , with this type of tool , you tap in in with a hammer , then unscrew it , DO NOT attempt to use the type that looks like a swirly screw, as this will only expand the soft brass, forcing the threads to tighten making removal impossible , as far as the adaptors are concerned, as I stated , you can use a brass tee, but the other fitings should be steel , you should only need 2 , a 1/8 npt close nipple and a 1/8npt to -4 an . The sender is inline with where it used to be and the -4 adaptor comes off at a 90.
In a worst case scenario you could pull the oil filter housing and drill and tap it (this would suck)
HTH
Wil