Macgregor Venture 15 73 banana hull

So I am getting ready to paint an old venture 15. Noticed some "flexing" in the side of hulls and on the top decks. So I bought some epoxy and set out to drill and fill. Guess what. Apparently Macgregor did not use a fiberglass foam sandwhich method. just fiberglass shell . Anywho now I have about 4 5/16 diameter drill holes in the side and on the top decks. Looking for advice from anyone who has gone through this same situation. Very little info on Macgregors and yes I have been to the mineresco page allready. Should I turn the hull upside down and inject the epoxy to add strength just let it go.
It would really be cool to get this thing in the water without it turning into a death trap. icon_confused
Thanks in advance.
Also thanks to all those that have taken the time to post to this site. Very informative.