I agree that 1/2 carafa seems like a lot. Why not use the 1/3# chocolate that is called for in the clone recipe below? This gets you closer as far as the extract is concerned.
(5 gallons/19 L, extract with grains)
OG = 1.073 FG = 1.021
IBU = 22 SRM = 30 ABV = 6.7%
2.75 lbs. (1.25 kg) Laaglander Light dried malt extract
5.33 lbs. (2.42 kg) Weyermann Bavarian Dunkel liquid malt extract (late addition)
1.33 lbs. (0.6 kg) Munich malt (10 °L)
1.33 lbs. (0.6 kg) Munich malt (20 °L)
0.33 lbs. (0.15 kg) chocolate malt
6 AAU Hallertau hops (60 mins) (1.5 oz./42 g of 4% alpha acids)
1 tsp Irish moss
Wyeast 2206 (Bavarian Lager) or White Labs WLP820 (Octoberfest/Märzen) yeast (4 qt./4 L yeast starter)
0.75 cups corn sugar (for priming)
I saw this recipe also but don't know where I'd find the Laaglander DME or the WEyermann Bavarian Dunkel LME?
Yeah I think the key is to find the appropriate subs. It looks like any light dry malt extract would work for the laaglander and try to find some munich liquid extract for the Weyermann?
I found this but have no idea if it would be a good choice or not