what is the bell-shaped sensor thats screws in to the back of the block behind the intake? does the intake have to be out to put it in?

 

No the intake doesn't have to be out. At least I don't think so. But may be easier with it out. I think you might be refering to the oil pressure sending unit. I could be wrong though.

 

thats what i thought it was but wasnt sure, i cant seem to thread it in b/c it keeps hitting the manifold, did anybody else with a 305 tpi have this problem?

 

there should actually be 2 senders back there. one (the bell) for the oil pressure guage. and the other (small two wire) for the low oil pressure fuel pump switch. these are attached to the block by a brass extension that comes up about 2" off the block. then turns about 45* and has a 't' attached to it. so that way you can attach the two senders to it. that is why the bell one hits the intake. here's a pic of it on my car when i was swaping heads. broke mine from the earlier engine swap. so, i got a 1/8" npt male to female 90* fitting. screwed it into the block. then found a 90* female to female with a 2" extension with male end. screwed that into the first fitting. voila! now i could put both senders back on.