To be truly 64-bit you shouldn't hard code the base address else things like ASLR won't work.
Also, using 'lea reg,var' instead of 'mov reg,offset var' will use rip-relative addressing (at least in ml64).
sub ecx,ecx
call GetModuleHandle
mov hinst,rax
...
lea rdx,aMybp1 ;mov edx,offset aMybp1
mov rcx,hinst ;mov ecx,IMAGE_BASE
call LoadImage