to run the oil line to the gauge, you need to put a brass tee into the block. on the back of the block, about six or seven inches above the oil filter is the stock oil pressure sending wire. it's a big nut with a wire coming out of the middle. pull off the wire, take off the nut and put a tee into the block. then reconnnect the stock sending nut on one side of the tee, and the oil line to the gauge on the other side.

tips:
-the nut is a 15/16, and you need to use a deep socket to clear where the wire attaches.
-remember to use teflon tape on all the threads, and don't over torque the tee; if it is made of brass it doesn't take much to break off the threaded part in the block.
-also, remember that if the tee has pipe thread, it doesn't need to be screwed all the way into the block, (i.e. the tee doesnt need to be flush against the block)
-since you have a mech. gauge, clearance behind the block isn't as much of a problem vs. a elec. gauge that needs a sending unit, so a standard tee should work. if the clearance isn't enough, a 90 degree tee will.

and in my opinion, as far as elec. vs. mech., if you install it right, you shouldn't need to worry about leaks. also, the readings on (any) mech. gauge (vs. the same gauge in elec.) are finer, and more accurate. but, that's just my opinion. good luck