C file functions in QB64 ???

[Ultraman]

I'd recommend putting the 64 bit and 32 bit code into their own $IF blocks that way no matter what architecture someone is on, the file will dynamically be ready to compile for their system, whether 32 or 64.
So something like
$IF 32BIT THEN
'insert 32 bit specific code
$ELSE
'insert 64 bit specific code
$END IF