I have used 424 in the past with no downsides at all. TCC, converters, no issues.
Infact, in a heavy duty application it is hard to beat. It will not break down like Dex 3 under severe situations like a trans brake launch, sitting on the verter stalling for to long. It will not save a failure, but it is better that "stock". Dex 3 can/does vaporize under extreme conditions rendering it totally useless.
Also, as a side note... in my experience 424 has slightly to marginally improved shift quality. Which is the reason some use type F to begin with.
If you feel the need, you could substitute a couple qt`s of 3 for F if you are so inclined. Some old timers add a qt of Synthetic 15w50 Mobil1 to their fluid, and swear by it.
B&M trick shift fluid is basically type F. (incase this gets thrown in)
I do not care for F as it seems to degrade any rubber seals. (but, if you have a leak you may want this, as it can swell them)
Mixing a few quarts of Dex 3 into 424 is a good idea, mainly to get color so you can tell if you have an oil or trans leak.
We all know, Buicks do not leak any oil though!
Good luck, HTH...
Brian