If I was rebuilding the engine I would remove the plug(s) and flush through.
As you no doubt are aware and for general consumption - cleanliness of the oil galleries is most important because you never know what is lurking inside especially after machining has been carried out. To enable the cleaning of the oil ways my engine has screwed in oil gallery plugs for all the galleries (horizontal and vertical) and are removed, rodded through with suitable brushes and flushed through with paraffin under pressure before reassembly.
Way back I did a post relating to fitting screwed gallery plugs to the 'A' Series with photos but it seems to have disappeared. With luck someone on here may be able to find it and repost
The photo below relates to fitting the gallery plugs (horizontal and vertical) for the oil pressure release valve dump passage back to the sump which is quite often forgotten about.
- Oil gallery plugs 1.jpg (94.51 KiB) Viewed 234 times