Thanks for your response, Robert.
Yes, the engine I have is the 25-inch block. Shipping to New Zealand is very expensive, hence why I would prefer an online version if possible. From what I've found so far it has the bypass filter system (seemingly a topic of hot contention when it comes to converting to a full flow system, which I am in the process of considering doing)
I'll have a read through your article attached - thank you for that.
The book I have does refer to 1957 Desoto's with the 250.6 engine, so I think I should be able to use most of that information for the 250.6 engine in my 59 Dodge, some things may be different, but hopefully the guy helping me re assemble the engine should find everything he needs in the one I've got. If anyone has an online version more suitable I'd love to have access to it!