I like the idea of the hops but if you want the true flavor of a German Radler you need to go with something like this:
9 lbs of pilsner malted grain
1 lb gambrinus honey malt
.25 lbs of weyermann carahell
1 oz german perle at 60
1 oz saaz at 30
1 oz saaz at 15
1 tab of whirlfloc at 5
Yeast: use saflager or Wyeast #2278 (czech pils)
if you want a more hybrid type of beer add 3 lbs of honey with 5 mins left in the boil (ames farm honey)
Once you get this completed and fermentation is over, rack to secondary and add golden grapefruit juice...if you cannot find any, next best thing is to buy golden grapefruits and juice them...even put rind into the secondary. Taste and adjust per your liking and document everything as you could come up with a gem here!!!!
Until we manage to attain more info on the actual procedure for this, I would avoid lemon lime from the grapefruit until we get more info...or better yet....try it out on a second batch =) its what home brewing is all about
The reason behind the choice in hops and juice is due to the historical nature of the Radler 2% ABV / 60-40 ratio of grapefruit soda to beer maybe 50-50 at the very least...the grapefruit flavor does not come from the beer. The Germans wanted something light in booze and something refreshing that they could drink for hours on end in the summer.