Yeah, use pumpkin if you want. You could always add maltodextrin for body, it would be less messy, but if you are purest, go ahead.
I'm not sure pumpkin chunks really add that much body. At least I didn't notice it, but hey, I've been wrong before and will be wrong again.
Here's the recipe I used:
BeerSmith Recipe Printout -
http://www.beersmith.com
Recipe: Pumpkin Wheat
Brewer:
Asst Brewer:
Style: American Wheat or Rye Beer
TYPE: All Grain
Taste: (35.0)
Recipe Specifications
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Batch Size: 5.00 gal
Boil Size: 6.13 gal
Estimated OG: 1.046 SG
Estimated Color: 3.8 SRM
Estimated IBU: 16.0 IBU
Brewhouse Efficiency: 75.00 %
Boil Time: 60 Minutes
Ingredients:
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Amount Item Type % or IBU
4.00 lb Pale Malt - Rahr (1.8 SRM) Grain 47.06 %
4.00 lb Wheat Malt (2.0 SRM) Grain 47.06 %
0.50 oz Willamette [5.00 %] (60 min) Hops 9.5 IBU
0.50 oz Cascade [6.90 %] (15 min) Hops 6.5 IBU
0.25 tsp Cloves ground (Boil 5.0 min) Misc
0.25 tsp Irish Moss (Boil 10.0 min) Misc
0.50 tsp Allspice (Boil 5.0 min) Misc
0.50 tsp Heading powder (Bottling 5.0 min) Misc
0.50 tsp Nutmeg (Boil 5.0 min) Misc
1.00 tsp Cinnamon (Boil 5.0 min) Misc
1.00 tbsp PH 5.2 Stabilizer (Mash 60.0 min) Misc
0.50 lb Brown Sugar, Light (8.0 SRM) Sugar 5.88 %
1 Pkgs American Wheat Ale (Wyeast Labs #1010) Yeast-Ale
Mash Schedule: Single Infusion, Medium Body, Batch Sparge
Total Grain Weight: 8.00 lb
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Single Infusion, Medium Body, Batch Sparge
Step Time Name Description Step Temp
60 min Mash In Add 10.00 qt of water at 169.4 F 154.0 F