Well, it's been a long time since I worked on a 261 but as I recall, the oil is routed directly from the oil pump to the filter, without entering the oil gallery. From the filter it is routed to the gallery. Any gauge location on the gallery or oil line should provide the same reading.

I believe if you look at the oil fitting coming from the block (pump) you are basicly going to be looking directly at pump output.

As a matter of fact, I bought 2 brand new short blocks from an Chevy dealer (who shall remain nameless) back in the late 60s. Their shop had installed both of these in a truck which came with a 235 with no filter. So, they simply plugged the holes. While setting the valves with the engine idling, 'it just died'. Locked up for lack of oil. I replaced the bearings after having the cranks turned and had an essentially new engine.