340 Flywheel

Does that engine still have the 340 cam in it? Is it staying?
That tranny has a granny gear in it,unsynchronized,IIRC; but I guess you know that. And a granny reverse, And terrible splits for a V8. Suitable only for a hi-torque/low rpm engine.
That engine and those gears are not gonna be friends.
Here are the ratios;
New Process NP435 Transmission Specs & Ratios
The split percents on the most likely to succeed tranny are 47-52-84.
Wrong tranny for an HO340. The 340 cam is totally Wrong for a truck.
What's your thinking.