New leaf springs on my 71 duster

Thanks for the information guys I'll check out Mancini I just was having a hard time finding some of the internet.... I wanted to leave spring that was going to put up with the abuse of the 340 I plan to put in it... Possibly throw the spring in now ( because the current springs now are pretty blown out old ) I was hoping that I'd be able to have at least bring that would work with my 8 and 3/4 when I do my upgrade I have the shock plates and all the hardware for my 8 and 3/4 just minus the leaf springs.