I have not had much to do with these 'new fangled' A series engines before, so I can not be 100% sure, but to get oil to the rockers, a drilling was made from this bolt hole to the oil gallery. To ensure that oil got past the threads, this hole was drilled to the major diameter of the thread far enough down to get past this oil drilling.
This then effectively reduced the available thread purchase length, so the simple fix would be to drill this hole deeper in the first place, which simply moves the threaded section deeper into the block.
This in turn would necessitate a longer bolt. One that had a reduced shank diameter to allow the oil to use the head bolt hole in the head as an oil gallery.

What does this odd head bolt of your look like again?

If you have a look at an A series cam, you will notice that there is a shallow groove around about 25% of the circumference of the middle cam bearing. In a running engine, with normal oil pressure, the rockers get only a 'squirt' of oil when this groove lines up with both the pressure side gallery hole, & the delivery side gallery hole, so here's the plan.

Crank the engine untill you have established that you have oil pressure in the block. Even a very low reading is OK here, so long as it is actual oil pressure. Move the rocker arms to one side a little & squirt some oil on the shaft where the rocker sits. You will need to turn it over to access all rockers in turn.

Start the engine. Watch closely to ensure that oil pressure is normal, then keep your eyes on the rockers. The engine will need to fill the hollow shaft with oil before oil is forced from the rockers under some pressure, but give it a moment & if you are worried, then just squirt a little oil on the pushrod sockets & valve tips while it is running. Unless something is seriously amiss, you should have oil flying all over the place in short order as a result of normal oil delivery.