Wow, with the duplication and the what-makes-a-person-themself theme, this is entirely up my alley.

And it was me, wasn't it? Not just someone called Mark Loddon, but me—me, myself? --Strong stuff.

Did it feel ineluctable that he would end up actual Mark? I ask because as you say, Frank is so very Ripley-esque. It's hard to imagine a memory wipe cleaning the slate entirely and making way for the better man that the 1945 Mark became.