You do have a perplexing problem.
The best solution would be, to relocate the temp sender to the intake manifold. If there is not a large enough, or any threaded pipe holes in the intake water runners, drill and tap one.
If you try to reduce the sender down in size with fittings, the sender would not be submerged in the hot coolant flow. Thus, you would get a very false reading. Reading much cooler then the actual coolant temp. Temp senders don't read steam.