I've rebuilt my diaphragm type vacuum pump without removing the radiator (it is easier with the radiator removed). Keep the check valves oriented in the correct direction because they are one-way valves - if you get them wrong you will have to take them out and reverse them. The Haynes manual covers the 1976-85 model years, so the directions for some operations are a compromise to cover all models/years.

Good Luck!
Tom

__________________
America: Land of the Free!

1977 300D: 300,000+ miles

American Honda: Factory Trained Technician & Honor Grad.
Formerly:
Shop Foreman;
Technical Advisor to Am. Honda;
Supervisor of Maintenance largest tree care co. in US for offices in Tex.