I know this is an old thread but I'd like to see this tool you speak of if still about.
Look up 'Boiler Tuber Cleaning Brushes', eg-
https://www.solobrus...e-tube-brushes/
There are a few different types, some for hand, some for power operation. Just those by hand will be quite satisfactory. You may not get a brush long enough to go right through the block, but if you come in from each end, you'll get them.
Don't go too 'fat' on the brush and I would recommend steel brushes, rather than brass or Stainless. You'll find after a few uses they may start shedding wires, at least with steel, a magnet works here. Also, after the final clean, use a small torch and look through every oil way, not just to check they are clean, but also that no wires are left behind.
I would also strongly recommend the Oil Pressure Relief Valve Seat be pulled, if for no other reason, so you can inspect the 3rd Main Bearing Oil Feed properly.