I have a 82 305 and just completed a lot of work on it ....I had the same problem you described ..header in the way of the oil sending unit above the oil filter
this is how i over came the problem....

the sender unit under the dist is for the computer and also effects the electric choke....however you dont need to have the unit installed to fool the computer and the choke...simply use a jumper wire across the terminals in the sender wiring harness.....

now you can relocate the other sending unit( located just above the oil filter) to the oil galley under the distributor....
I had to use a brass nipple 2" long screwed into the block and then mount a 45 ell bow to mount the other sending unit into...clearance is tight but will work just fine...no binding or rubbing when engine torques up

be sure to plug the oil galley on top of the oil filter using quality sealant...
its not easy to get to again ...once the header is installed...and its a long way back in to remove the header just to repair an oil leak

hope this helps