Some more info I just completed my 2000 silverado 63" leaf spring install last night.
The front spring bushing has a 5/8" diameter bolt hole so you will need to drill your spring hanger to match.
The rear leaf bushing is still 9/16" so that hasn't changed.
Also the center pin on the leaf pack is a little larger than 5/8" so the ubolt plate center hole will need to be reamed out slightly to fit.

I have a semi light flatbed on my truck 300-350 lbs the 00 silverado pack I am using is a 2 leaf pack with a overload.
I am using bud built 8" shackles and the spring pack makes the truck sit level with the front and I believe the front springs are 4" procomp springs they have sagged some and are actually about 3" now.
I am able to completely stuff my rear tires they touch my flatbed tray.