This is what I'm following: https://en.bitcoin.it/wiki/Wallet_import_format

The source code for the hex creation (see 'ToString') is here:

https://github.com/bitcoin/bitcoin/blob/master/src/bignum.h

As I'm just learning to program, I'm having trouble following the C++ code so instead trying to follow the wiki process. If they are concatenating the int(64) with something else, it's difficult for me to tell.