Just a few words on transmission to centerline of crankshaft alignment and vibration/pump, bushing failure as I see it was mentioned a few times in multiple posts above. This info may be known by many car enthusiasts or may be new info to some but is important to understand. The centerline of the trans input/converter/crank is all indexed off the Dowel Pins on GM products (others as well) not the bolts or bolt holes. There is also a “pilot” surface machined into the back of the crank concentric with its rotation although it is seldom referenced and not called a pilot bushing or bearing like a manual trans. This is a one to two thou slip fit for the large center nub on the front of the converter, and the dowel pins are a snug interference fit to the trans case. The center of the crank and trans are indexed in space vertically and horizontally within a thou or two so as to not have misalignment vibrations from the factory and to allow service replacement trans to be installed without these issues. During service-engaging all three steps of the converter and pushing it back an additional quarter inch or 3/8s allows the trans to center on the dowels, and with the rear of the converter centered on the shaft/pump/seal, be pushed forward to fit the front nub nested in the crank. This is what aligns the converter to run true to crank and trans! Not the converter bolts. I would be suspect of any “kit” that does not have snug fit dowel pins on the adaptor plate and is not CNc or quality controlled to centerline from them on each kit .Looking at the pic of the GM kit on the second link- it seems to have an alignment cup machined in the crank adapter but relying on the bolts to center it concentric seems to be playing Russian roulette also. I would be checking it for spec on the converter snout before installing, then performing a runout check to its alignment bore inner surface with a dial indicator with that crank adapter installed while spinning the crank by hand, and checking all centerline to dowel alignment on these parts. There are other things that affect crank centerline such as remachining crank bore for spun bearing (is raises the centerline) and others I will not get into here. Do a search for “offset dowel pins” and measuring manual trans input shaft to crank runout and you will get more info! Good luck.
BTW. The crank adapter on that kit looks like it is an inch and a half or two inches deep. As I recall the V8 engine has a deep flange cast into it as part of the bell housing and this spacer depth required due to this spacing of a GM (or any) trans further away from rear of crank. As such-any rust,nicks,debris,bending,or out of true of the Packard crank flange will be multiplied by the length of this spacer. Another wobble, vibration threat.
