The LC8 motors are really bullet proof with the exception of the water pump. I would not strip the bottom end open unless you have problems.
Athena makes good stuff. It's my first choice for gasket kits. Moose also makes good budget kits.
Frankly, before putting new rings on the motor, run a compression test. If it's all good, check the valve shims. If they are not at minimum, then I would call the motor good and would not take the risk of putting new rings in.
As for the base gasket, the seal is not under heavy pressure. I would apply a bead of 3-Bond 1184 on the case, let it tack up for 10 minutes before applying the gasket. 1184 is the stuff I use when assembling case bottom halves that don't have a gasket and it holds up well.
Do perform all the TSBs on the motor including the rotor bolts. Upgrade the water pump with the new shaft, seal, impeller, and side cover. Replace the counter balancer seal along with any other external seal like the shift seal and counter shaft sprocket seal.
I converted to a vacuum pepcock a long time ago and don't have to worry about it again.
My R/R started to go out and overcharge the battery. I went with a kit from http://roadstercycle.com/
. Might be a good idea to have one on standby.