1975 OMC 165hp Sterndrive,

[Lundrv52]

has anyone seen or know of away to attach a gas trolling motor to the out drive?

 

[Droid]

It would need to be on a bracket (custom made) that is cantilevered quite a way back to clear the lower unit. In my opinion the stresses & all would not be in your best interest.
It would also potentially hit the transom when tilted up.

What do you plan to gain with this cumbersome & expensive idea? Extra weight, wear and tear, more maintenance?

That inline 6 will idle plenty slow all say long if trolling is your idea.