Rallye dash conversion

Oil pressure sender for use with a warning light:
PS11T_Front__ra_p.jpg

Oil pressure sender for use with a gauge:
PS59T_Front__ra_p.jpg

They're not interchangeable.
You didn't say if your fuel sender is an original factory one, or an aftermarket replacement; which are notoriously inaccurate. Lots of threads on here on that subject.