The sticker on the valve cover says:

Engine Family 351M/400 EGR
Displacement 6.6L (400 cid)
Spark Plug ASF-42 Gap .042-.046

It has a chart with some setting info on idle and kick down etc. Then it says:

NON CATALYST

D8TE-9C485-ACA D009

This engine conforms to U.S. Environmental Protection Agency Regulations Applicable to 1978 model year gasoline fueled Heavy Duty.

Since it is a non-catalyst, isn't it possible to simplify the vacuum routing?

Since the vehicle is over 24 years old, my State does not require smog testing on it.