I agree that the Ronnestad workout looks extreme. I created it based upon the recommendation of another over 60 cyclist but have not performed it. Your suggested mods would be good. The Ronnestad method of short 30/15 intervals (over 4 min. intervals) was tested several years back and showed some good improvements. Discussion here: The 30/15 Interval Enhance Performance in Elite Cyclists | Wattkg.com. Extended TR forum discussion here: Empirical Cycling Podcast “Why Not Rønnestad 30/15 Intervals” aka Brasted, which includes that TR’s Brasted workout follows the Ronnestad method.