I doubt that you will find what you need as a kit, as it seems there are more junker Packards with salvaged engines than the other way around. To me it doesn't seem that full rebuilds are terribly common, so you'll probably need to source parts individually if that is all you need.
However: FULL rebuild kit is for sale for $1619:https://www.kanter.com/packard/pac-556.html#5[/b] •8 pistons with pins and clips •piston ring set •overhaul gasket set •cam bearings •main bearings •rod bearings •valve springs •timing chain and gears set •freeze plug set •valve lifters •engine pre-lube