Saw dust or generic, unscented cat litter (pure ground clay)

I wouldn't bother with the filler. the N P and K are in the right proportions (or at least really close) so you should just adjust the amount you use.

If you skip the filler, you've got something that's about 25-4-15. Instead of using 5 lbs per 1000 sq ft, use 4 lbs and you apply the same amount of N P and K.

Filler is not fertilizer. You need fertilizer. Instead of thinking in terms of filler, just adjust your numbers to bring the total weight of the components up to 7.3. And don't be anal about getting exactly 7.300000 pounds. Something like 6 pounds of N, 18 ounces of P, and 6 ounces of K would be much closer and still put you in the Lawn Nut category.

It is now fall. When was the test done? Was it done with fall in mind? Under a chemical fertilizer program there is usually one app (of a different formulation) in late spring and two apps of high nitrogen fertilizer in the fall. 1/3 of the total annual nitrogen goes on in late April or May with the rest going down now(ish).

I don't know where you live but generally speaking, I would apply the first fall app now and the second one around Thanksgiving as long as the grass is still green. Then in the spring you can deal with your blend.

Similar situation: Soil tests show that, in Fall I should apply these fertilizer mixes:

36,000 s.f. front lawn (24-0-11 @ 4 lbs per 1000 s.f. ) and

15,000 s.f. back lawn (31-3-10 @ 3.5 lbs per s.f.).

I am having trouble backing into the figures Joet gave, above. Can any one give me an idea of what ingredients to buy and how to mix to get these mixes? Thank you!

I don't recommend trying to match numbers like that, because you never can.

The front is recommending normal levels of nitrogen, 0.4 pounds of potassium. The back is normal nitrogen, 0.35 pounds of potassium.

That's actually kind of a small amount unless they recommend repeating this, in which case there's probably an easier way to do it in one or two shots. Can you post an image of the test?