I would come help you but that is a long drive on a weekend unless you want to get up at 2-3am when I am coming through the area during the week, I am usually pretty good a getting things running right. but first off I would like to see a little more timing in that like around 8-9 but also check that the advance is working, and what is your total advance.
Next which carb are you running as I remember without looking you still have the 2bbl on that right? if it is the stock one from the 360 it's too small that is like 450cfm, you need atleast 525, and yes you will need to rejet it some.
The tail shaft problem is not a problem remove the drive shaft unbolt the yoke and take the bolts out for the tailshaft it comes right out, drive the seal out, and I would also look it should have a bushing in there, replace that also most times when they start leaking it is because that bushing has worn and allows the shaft to wobble just a slight amount which takes out the seal, also when puttingit back on I don't use the gasket most times (started doing this when I had trouble getting the gaskets from the adapter to transfer case) when I worked for GM we used an anarobic sealer, but on the race truck I have been using blue rtv silicon, and it doesn't leak.