Let me start with I'm no expert. But I have had the good fortune to fish with a few.
I have rigged my lead core lines with 10# mono backing but plan on using fly line backing (thin dacron) this year. I attach the backing to # 10 Spro swivels. They are rated for 35# and are high quality. You can see them here.
I pull back the dacron backing about 4-5" and remove the lead from inside the lead core then tie the dacron coating directly to the swivel. I then do the same on the other end which then is attached to another swivel that connects to the 50-70' of 8# mono. I then use yet another swivel to attach the 10' of 4-6# fluro which I tie directly to the lure.
These swivels are tiny and will go easily through the guides.
I am in the same boat. Ha! Ha! As I am going to be installing a Riviera Mast on my boat which I have some questions about but will post a new topic as I don't want to hijack yours.
FWIW, You may want to search the archives for leadcore and trolling masts for some ideas.