I have expereinced the same situation....

BUT... I was pretty darn sure that the 261 has a full flow oil system.... in fact if you plugged the outlet and inlet with pipe plugs and fire up the engine you would have no oil circulation....

....so I have read and not about to test out on my new 261...... any comments from real experts as I am not.....

My dual filters are installed even/level with the clear HD oil lines going out of the block and attached to the testing frame using about 36 inches of heavy clear lines. Since I did not fire up the engine before Winter I mothballed the 261 by running up the pressure with a 3/8 HD electric drill..... got the oil pressure up to 42 pounds on a mechanical gauge....all the while spinning the engine with the starter w/o plugs.... one line blew off as I had not installed any hose clamps not thinking that the cold oil could develop that much pressure.

Now for the clincher.... within an hour oil had drained back into the block... repeated the process twice... after installing hose clamps and refilling the engine...same results... I am sure the filters are still full...BUT the lines have air both sides of the filters.

How critical is this situation???? would I have the problem if I used opaque lines... no see no worry????

The Original GM filter was a long canister held to the intake manifold...fairly high above the oil pan.... some military model similar to mine had the oil filter canister mounted sideways on the frame... somewhat lower than the edge of the oil pan.....

So what is the best location... high or low...??

....and Jason.... what brand of filter have the anti flowback valve.... my remote is set up for standard PH 8 long spin on filters...common on Chryslers and some older Fords.....

Thanks for you help..

Bob C.
CMP Heaven
The Hammond Barn