Two toggle turbo help please

[Ahva]

I have been trying to figure this out for a day now and I have not even come close I need a script that when I press F8 it spams F8 at 40ms and when I press F9 it spams F9 at 40ms I also need it to only allow one to run at a time for example if F8 is running and I press F9 it will stop the F8 and start the F9 key and the same the other way and then the final part is I need 3 mod keys that when they are held will pause the rapid fire for the F8 or F9 key I am using and when I let go then it will continue with the correct key the mod keys are shift, control and shift and control together any help would be greatly appreciated thank you.