Large Advent, Restoration Quests

I'm attempting to restore a set of the large Advents.I have two sets.One built in 1974 w/fiberglass inside.The other from 1976 or 78 w/sponge foam inside. The woofers need new surrounds.Was sponge foam used inside
these speakers for dampening ?Do I have to use surrounds designed for Advents or can I use reg.10"surrounds turned over to invert?Any suggestions on beefing up the crossover?Thanks!for the input/ help.almac