Rotten Engine Logs

[easterly38]

I'm new to this forum, so forgive me if this has been covered before.

I'm working on an Easterly 38 and recently discovered the engine logs are completely rotten. They were wood encased in glass, now they are water, mud and termites encased in glass. I have cut the tops off the glass encasements and removed all the debris. My question is, can I fill the encasements with fiberglass and resin, drill pilot holes then fasten the motor mounts with lag screws? Will the threads hold? Or, do I need to rebuild by epoxying more wood inside the fiberglass and glass over the tops, as they were originally built? The all glass idea apealls to me as it won't rot and I won't ever have to replace any wood, but I don't know if the all glass approach poses unforseen problems.