That grain bill is fine.
I use 75/25 Pilsner/Kolsch malt with 029.
I have never seen Kolsch malt until now. Would Vienna be a reasonable substitute especially in smaller quantities?
yeah, what is Kolsch malt?
I found this on Northern Brewer:
4.5° L. From a maltster co-op based in Osthofen, near Köln, this malt is used by some of the brewpubs in that city to make their trademark ale. Kölsch malt has a light, sweet and extremely "German" flavor and aroma with a little bit of biscuit character. We've had good results using a multi-temp step mash with Kölsch malt, but a single infusion — although not traditional — works as well. Style nerds please take note: the maltster rates the color of this malt at 9 EBC. If you use 100% Kölsch malt for the grist of a Kölsch, you will be within spec according to Eric Warner's Kölsch (7-14 EBC, or 3.5-7 SRM — p. 51), but definitely on the dark end of the BJCP guidelines. If you are brewing for a competition, you may want to incorporate some pils or wheat malt into the grain bill to dilute the color.