Step 1:

Move the Assets folder inside "BNSF SD70MAC Bundle" into your main Railworks folder. It should be in C:\Program Files (x86)\Steam\steamapps\common\RailWorks. 

Step 2:

Go to Assets\trainsanddrivers\Alaska\RailVehicles\Diesel\SD70MAC\Default\Engine and copy SD70_Mac01.GeoPcDx

Paste into Assets\trainsanddrivers\Alaska\RailVehicles\Diesel\SD70MAC\BNSF_H3\Engine

Step 3:

Go to Assets\trainsanddrivers\Alaska\RailVehicles\Diesel\SD70MAC\Default\CabView and copy sd70cab.GeoPcDx

Paste into Assets\trainsanddrivers\Alaska\RailVehicles\Diesel\SD70MAC\BNSF_H3\CabView

Then repeat the process for the H2 unit