Hi, as you probably know Lego Universal Joint 3L is not the strongest one in case of high power aplications. Some time ago I had modified my 9398 Crawler with 2 XL motors and they was breaking joints easily when one wheel stuck. I was looking for solution and found RC boats universal joints on aliexpress (3mm hole). It cost about 2-3$ each or less as far as I remember. So all in all it seems that it can work. Only thing you need to do is drill "X" openings to fit axle.
Here is a common view on my 9398
Axles are glued to joints and they are designed to replace original 9398 setup.
they have same length using bushes (top part of 1L bush was cut and placed on axle)
Hardest part of converting - drilling holes.
And here is a result:
After testing performance is now pretty cool, additionaly they're lubricated with silicone spray so I don't have to worry about friction and spare Universal Joints in my pocket when driving.
Hope you enjoyed my custom made cardans :)