Hi Albert, Sorry For The Late Relay...
First, thanks for the nice compliment, I've been playing with 128s for many years (I've owned six so far, more if I count cars bought just for parts), but I'm still learning more about them, as are others here on this forum. The earlier 128 sedans and wagons came with front coil springs that had 8-3/4 coils, while the later 128 sedans and wagons came with front coil springs that had 10-1/4 coils. Interestingly, the spring rates for these two different springs was roughly the same, as they used different diameter wire to fabricate the springs, although they did provide different ride heights.
I've dismantled two 128 SL models (one '74 and one '75) and both of these had front struts with the 8-3/4 coil springs, however I suppose that it is possible that both of these cars at some point had the front strut assemblies replaced with sedan or wagon assemblies, as parts swapping from salvage yard cars was quite common back in the day.
I'm almost certain that the later 128 3P models used the same 10-1/4 coil springs that the sedans and wagons used, but the earlier 128 SL models sold in the USA may in fact have been built with the 7-1/2 coil springs as Dwight and others have indicated, so I stand corrected on this point.
The most straightforward method for effectively lowering the front of a 128 sedan/wagon/SL/3P is to swap the entire stock front strut assemblies for those from the rear of a '74-'78 X1/9, changing only the top strut mount for compatiblity with the 128 unibody. This not only lowers the front to what most folks would consider to be the 'normal' height rather than a 'lowered' height, but it also stiffens the front suspension by a proportionate amount to prevent bottoming at the lower ride height. Road manners are excellent, even with oil cartridges.
In my opinion, installing rear X1/9 springs on the stock 128 struts is do-able, but you have to use the shorter X1/9 rear strut bump stops, and even then a significant bump will cause bottoming too early, and so it is best to use the complete rear X1/9 strut with the 128 top strut mount. I've been using this setup for years, sometimes with stock rear X1/9 springs, sometimes with custom springs to suit the character of the particular 128 that I have.
Early rear re-buildable X1/9 struts are getting a bit harder to find these days, so if your 128 struts are the re-buildable type (with spin off top collars) you might consider having them cut and shortened to replicate the height of the early rear X1/9 strut, so that you can load them with inserts made for the X1/9, afterwhich you can check and adjust the camber if necessary, typically the camber will need to be altered to the negative by a degree or two with this methods, while the stock early X1/9 rear strut camber is just about perfect for the front of a lowered 128.