There is no 1970 Engine Manual. There is a 69 Manual. With that manual, the 70 Mustang Service Manual and the 75 edition of Ford Car Parts (aka MPC), you could get about all the info you need.
Jim
Unfortunately the 69 engine assy manual is not helpful for many areas of my 70 Boss 302.
The service manual (the multi-volume set) is hopelessly vague in specific areas. There are numerous changes from the 69 to 70 Boss 302 engine front dress (block forward including cover, pump, etc) including the change from 3 to 4 bolt dampener.
Most of the accessory drives and brackets have changed.
I've used the many illustrations in 75 MPC, but details are lacking in areas.
I've owned this version of the MPC for over a decade back when you had to buy the CD for $75! It does have a nice indexing scheme, however.
To get an idea of my latest issue simply view my latest post in the Boss 302 section.
Sorry, just venting ...