K frame and coil springs

[BannysSSP]

I picked up a very nice OEM K frame and steering rack and was thinking about swapping out the one in my 87 SSP. I do not know what year, model, or engine the K frame was removed from but it does have the two frame braces that I believe were unique to converts. There are two stampings on the top side rear of the two K frame rails, one side is 12 15F2, and the other 12 22F2. Thoughts/suggestions on this replacement project? are there differences in the K frames depending on the models... other than the springs? Which brings me to question two... my door FSS indicates the springs on my SSP to be PP front and SS rear. I did not find these codes listed in the service manual? I located an old crunchy sticker on one of the front springs on the SSP and this is what I could decipher,

74. 5/8 435
MON
E5 SC
5310 NA

Does this possible cross with the information on the FSS? Ideas on the proper correct replacement springs?