Hamilton A05H21 vs ETA 7750

[Peashooter]

Need some info as I am embarking on a franken adventure. 

My A7750 has been showing 1-2 issues (wouldnt start even after winding when left with zero power reserve). 1st time it came back alive was when I pushed the chronograph and the 2nd time it happened was last Monday whereby I had to knock it on a wooden table.

I just bought a Hamilton A05H21 movement which I was told is a modified /upgraded ETA 7750 with (1) 60 hours power reserve (2) improved time accuracy.

Anyone tried this swap before? Any pointers/tips on what to look out for?

[Peashooter]

Watchsmith had no major problems swapping out the movements but he did mentioned that the case has to be slightly tweaked, didn't pushed him for details. So you guys can consider taking this besides the base ETA7750 model.