8Bore - what a lovely rifle indeed.
I am sure that using the 3 dram load will work wonderfully.
A mixture of good Beeswax/Vaseline, 60%/40% is a very good one - or simply use SPG or Lyman's Black Powder Gold lube.
The Old Enysford you have chosen should work just fine - or Swiss 1 1/2F.
I am sure that working with this rifle will be a pleasurable endeavour.