mounting engine mounts to stringer

All boat owners know to well that one repair always leads to others. Mine started off investigating an engine problem and is now leading into a restoration project. I attempted to remove the starboard engine mount from the stringer, attached by two corroded lag bolts, and both snapped off. I drilled what was left and had a failed attempt to use a screw extractor to remove the remaining. I then did my best to drill out the remainder of the lag bolts with a depth of approximately one inch by 3/16 in drill sized hole. I didn't feel comfortable going any deeper, although it appears that there is more of the bolt below. My questions are: 1). Got any ideas for a custom mount to attach the engine mounts? 2). How deep are the lag bolts normally placed to be sturdy enough to keep the engine from shifting? 3). Are the bolts normally epoxied for more strength when originally installed? This boat is a 1977 Sedan Bridge with a 350 chevy Mercruiser 260 power plant. Any information shall be greatly appreciated.

If they were severely corroded it means theres some moisture present. The best thing to do is open up the stringer area, remove the bad wood,
get some poplar or oak block cut to size and resin or epoxy it in place. Then add some fiberglass cloth to repair the stringer opening.
Set the motor in place , locate the new holes

Bt Doctur said:

If they were severely corroded it means theres some moisture present. The best thing to do is open up the stringer area, remove the bad wood,
get some poplar or oak block cut to size and resin or epoxy it in place. Then add some fiberglass cloth to repair the stringer opening.
Set the motor in place , locate the new holes

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Thanks for your help. Do you know how deep the lag bolts are set?

most are between 3 1/4 and 4 inches