I want to try some low power loads for the 243 and I have some IMR 3031 and some IMR 4350, any idea how much of either to reach about 2000-2200fps with jacketed bullets?

Depends on what you are using for a bullet...any of the minimum loads at my pages should put you in that area...but especially the ones that use SR-4759

The standard advice is not to use anything slower than 4895 for reduced loads. I use IMR 3031 in my .280. Using magnum primers, I loaded down from the starting loads looking for good accuracy. It was easy to find loads in the .4-.7 MOA range.
Usually a direct ratio reduction will get the velocity you want. If so much 3031 produces 3000 fps., then roughly 2/3's will produce 2000 fps.
Good luck. Reduced loads are quiet, recoil much less and are very easy on brass. Make good pelt and practice loads. E

Believe it or not, Blue Dot is a good powder for reduced loads in rifle cartridges. I don't know about .243, but I've used 12 grains of Blue Dot with 50 grain bullets in .223 with good results (max loads with normal powders are 25 to 30 grains). It works better with lighter bullets. One reason it is good is that it is relatively bulky.

Hodgdon has "youth" loads for most popular rifle cartridges they use H4895. I bumped them a little (still below regular start loads) and had good results. I was using 80 gr Rem PSP at ~2600 fps.

Don't try 4350 for reduced loads. The Hornady manual and maybe others recommend against light loads of slow powders in the .243 case.