The guy that ported TurokEX(This version of Turok) also ported DOOM 64 EX to PC. He had to reverse engineer the entire game because the source code was lost for DOOM 64(making a regular port impossible) While developing the engine for TurokEX Nightdive hired him and that's why we have Turok 1 and 2 on consoles, which use the PC versions as a base.
https://doom64ex.wordpress.com
Meh, as good as Doom64ex is, it's no Doom64. I wish the source code was not lost :/