There isn't a 64-bit P3D SDK v1.4 version.
I do not work with 3DSMAX, but just out of curiosity, I looked this old URL up on:
Wayback Machine - Internet Archive
...and found this:
"More is Better – 64-Bit Modeling Tools Released
The Prepar3D development team is excited to announce the release of an update to the Prepar3D v1.4 SDK – which includes new 64-bit modeling tools. The Prepar3D team heard the feedback on our forums that modernized and updated tools were needed to build more dynamic content, and the development team partnered with many leaders in the Prepar3D development network to implement their feedback. The result of that hard work is a free update to the Prepar3D SDK that allows developers to create much richer and more dynamic content for Prepar3D.
You can download and read the release notes for the updated SDK here, as well as download the patch here (note: you’ll need to be logged in, and have already installed the v1.4 SDK, this is simply a patch you’ll install over your previous 1.4 SDK installation).
But don’t take our word for it, here is what members of the Prepar3D Developer’s Network have to say about the updated modeling tools and SDK features:
“This new set of tools provided by Prepar3D really were spot on. This means for us the possibility to produce better quality content and much quicker. Right now we have to model in 3D software such as 3D Studio and then export each aircraft to GMAX which is an extra step that we will not have any more. More over the new tools doesn’t have a 64K limits polygons per material which means no limits for reproducing details generating an even better flight experience.”
“At first, with Max 2012 32bit, we were limited by the antiquated ESP export system, only having the ability to export 65K Polygon models at a time, having to ‘knit them together’ into full models through another program, having to reboot Max with each export of each segment of a model. But Team Prepar3D saw our needs for a new, updated exporter system and set to work to make us a package that we could really use, and this is it. Now, we can run Max, CS6, and P3D all at once, not having to reboot Max, all running on a 64bit computer, without having to shut off side systems, exporting smoothly without worry, and testing.”
“Fantastic news on the tools, I managed to export a 450K+ poly Zlin Z50 LS the other day without breaking a sweat!! Runs lovely too.. I’m now saying goodbye to Max 2008 and the old plugins.. The changes to XtoMDL are fantastic and really do turn on a light when it comes to compiling larger more detailed models.”
–IRIS Flight Simulation Software"
I also found this download still available via a link from the web page above:
When I use Inso / Avantstar QuickView file viewer, all files in my recently downloaded / installed P3Dv1.4x 3DSM2012\Plugins\ folder are reportyed as 32-Bit except:
[Prepar3D SDK 1.4.4747.0 install path]\Environment Kit\Modeling SDK\3DSM2012\Plugins\BaseTypes.dll
...which could not be viewed in default mode.
This raises the question as to whether one must still download and apply the above cited 64-Bit "patch" or if it is already incorporated in the P3Dv1.4x SDK.
Hope this helps.