1973 Duster 9 inch brake upgrade questions

I'm currently working on a 73 Duster 318, with 9 inch drums in the front and 10 inch drums in the rear. I'm figuring it didn't come that way ( should be 9 all around right?). So I'm good with the 10 inch rear, but trying to figure out what to do in the front. Now I've been looking at Scarebird and they don't seem to have anything for 73 up. Now it's 5 on 4 lug pattern and I like to keep it that way, but what low cost options do I have for a disc set up that is still 5 on 4? With the big ball joint