2019.1.9F1 - JDK / SDK / NDK Selection

Afternoon Folks

Running V2019.1.9f1 on Slackware-Current

Using Unity's Downloaded versions of the above work fine BUT

I wanted to choose my Own JDK, SDK, NDK

JDK works fine using Oracle JDK 1.8.0_u211
SDK Is latest downloaded from Android.com
NDK Version is 20.0.5594570, installed via Android Studio - SDK-Manager

Unity/Preferences
Now if I want to change oracle from Unity's version to my above it works fine
Pointing the SDK to /home/user/Android Works fine
If i wanted to change the NDK version to the above I get the error
"NDK 20.0.5594570 detected. Unity requires NDK r16b(64-bit) (16.1.4479499)

Error is fairly self explanatory, but is their a way to force the usage of V20 anyway, the error message only gives me a Browse, or Cancel, no Continue etc

Their is nothing stopping me using Unity's version of any of the above everything works and builds fine, but surely I should be given the choice to use my own downloaded versions and be given the opportunity to diagnose my own problems?

Another problem I have encountered, If I select my own versions of SDK, JDK when I restart Unity the Tick box next to them are ticked again thus forcing the use of Unity's versions. Anyway around this?

I know asking for help on anything other than Ubuntu is not going to achieve much but are the above more bugs than help required?

Regards