Chrysler built distributors use different springs than the mallory built distributors.
Older p-part light springs are going to be for the chrysler built distributors. The only spring kits I am aware of DC/MP selling for those distributors were very very light springs.
Tach drive distributors were sold with a very light primary spring and a very heavy long loop spring.
Mallory YH kit works with Mallory built p-part distributors.
However the Mopar Performance kit comes with more springs and a more complete chart of spring rates.
At the moment I can't find the digital pics I took of the Crane and Chrysler springs.
Below is a pic of the springs for the YH style distributors. And this is a
link to some more pics of the two styles of MP-DC vacuum advance distributors.
Rates for the Chrysler style internals based on my measurements and calcs;
Primary SpringsCrane Blue: 24 lbs/in, .6 " loop to loop
Crane Silver: 13 lbs/in, .6 "
Crane Yellow: 11 lbs/in, .58"
A-1 brand Rebuild: 8 lbs/in, .72"
MP Vac Dist: 7.2 lbs/in, .72"
Tach Drive: 1.26 lbs/in, .72"
P 2932675: 0.68 lbs/in, .7"
So if you use two springs, double the rate. If you shorten the slots, the same spring will supply less force unless you change the over length by bending the loops. This is why a lower rate spring does not always quicken the advance in the rpm range you're looking for.
Secondary Springs A-1 brand Rebuild: 45.8 lbs/in, .92"
MP Vac Dist: 113 lbs/in, 1.0"
Tach Drive: 174 lbs/in, 1.09"
As best I can tell, the concept behind the tach drive arrangment was for easy starting and stable advance starting from 800 or 1200 rpm up depending on which primary spring was used.
Just for comparison, the YH type primary springs range from .55 to .68" and have rates from 1.7 to 7.6 lbs/in (or 13 #/in depending on whose numbers you go by). So it looks like they might work on the chrysler made distributors with maybe a little tweaking of the loops. But the loops of the YH secondary springs are probably too narrow to work on the chrysler made distributors.
