AFN 134-200 hp and 02A tranny setup question

Guy's,
We have a question .... 1st of all .... is this the right place to ask?
The situation as is:
Polo 6N open air (original 5 speed diesel 64 hp) now equipes by us with an AFN 1.9 TDI - tuned to 143 hp equiped with the original combination transmission type 02A CYP (I guess this combi was from the Golf III TDI 110 hp).
The problem:
When driving in the 5th Gear we very quick reach the red area at 204 km/h with power being available. Problem immedeately is that the engine is getting hot.
Not that we love to speed so fast (I am lying ) but we want get out of this "dangerzone".
Solutions?
1.) We have heard one option could be to exchange the 5th gear from CYP configuration to ASD.
2.) switch transmission in full to ASD
3..... to 10 ? Your suggestions.....

What do we want to do with the car:
This car we bought new. Wanted to sell it but family doesn't agree - so we optimized it ..... we want to drive on the street but will have the option to go on the track with this car ......
We changed engine, exchanged al brakes for bigger ones (G60 in front - gti brakes back) - we will built in a safety bar (when we find an original one).

Thanks in advance for your advices....

Cheers from the Netherlands

What is the temperature? Coolant reading from computer? Do you have oil temperature also?

What rpm is the danger zone you speak of?

If you Change 5th gear, to lower rpm by 300-500 rpm, why not test it at that speed/rpm and see what temperatures are.

Thanks you are right ... my rpm doesnt function due to a mistake of me in the electric but when driving 180 km/h it is no problem at all so I presume a changed 5 th gear should be the solution beside changing the thermostat from 89 to 71 degrees celsius.