Dizzy recurve for 440 MH input

'77 is prob pre-cat for 49-states in truck. '78 too but this is all asumes it still has the factory distributor.

It works something like this for pre-cat cars.
For the CAP and CAS Chrysler retarded the initial timing and used a quicker, long advance so off-idle everything was close to the same as non-CAP.
This was coupled with lean 14.2:1 idle fuel mixtures. The idea was to reduce CO and HC at idle.
Then they played with some different methods to reduce emmissions on deceleration.

In the 70s things changed just about every year, but you may find initial timing is retarded compared to a similar mid 60s non-CAP truck engine.

A mid 70s vehicle, especial a truck, may have a coolant temperature switch to boost timing at idle if the coolant gets hot. These switches allow manifold vacuum to the distributor vacuum advance.

By '77 on truck there might be EGR, but hopefully not the vacume advance delay system.
If it has a timing delay on accel, that would be worth experimenting going without. Came in around '74 for the cars.
EGR feeds in hot O2 so I'd go with the factory timing on an EGR equiped engine.
Make sure its hooked up right. No EGR cold, No EGR at idle hot or cold, No EGR at wide open throttle.

Timing is advanced more with the slower the burn. A heat soaked engine should have pretty good burn. I think thats where RRR and TMM are coming from.