Zwift .gpx to Workout


I have a gpx file from a mtb race that a friend of mine did last year. He is a strong cyclist with an FTP around 350. He has a quark and the avg watt was 331. Weighted avg power was 367w. His weight is about 76-78kg. About the same as mine.

I wanted to make a workout out of his race and ad it to zwift with whatsonzwift and have the same numbers as him. But when i convert it with my weight and my ftp set to 330 the workout seems very low compared to his times in different power zones. If i raise the ftp more the time of the workout becomes to fast. The only way to get his watt/avg is to make my rider about 180kg… then the time is the same as his finnishing time and the same watts.

Is there a way to make it identical as the output in the file?