Another user on a thread recently mentioned using the 265 FTX in 44mags - but I believe he was shooting a break action single shot (TC?). I'll concur with the expectation you'd have to trim the cases VERY short to function with the longer ogive of the 265grn. For Marlins, a guy has to trim brass below typical "trim to" length when using the 225 FTX, which is considerably shorter than the 265 FTX meant for the 444.
I'd also question the designed expansion velocity for the 265grn vs. the horsepower available when shoved deeply into a super-short 44mag case.
And of course, a guy has to question whether the velocities attainable with the super-short 44mag cases will be sufficient to stabilize such a long bullet in the Marlin barrels. I haven't had issue myself with them, but I've heard a lot of guys complain about lack of stability in the 300grn XTP, which could be seated longer to allow greater powder volume than this 265 FTX, and the XTP is shorter to boot - so any rifle which has problems stabilizing the 300 I would expect to have worse problems with the 265 FTX.
If they'll feed, or the carrier could be modified to let them feed, and they match up to the chamber dims well enough for leade, it'd be interesting to see how they do. But considering these points above, I'd be questioning myself - is it really worth trying some odd-ball combination when there are lots of other proven options out there.