I dont know how to tell by looking at it, but Normally they are externally balanced. They usually use 400 flexplate and balancers. There are some cranks that are intearnally balanced for 383's but those get expensive. How much did the motor cost you or was it in the car when you got it?
Ben
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86 GN - GT67, B&M Trans Cooler, Built Trans w/ many upgraded parts, 3200 Vigilate Stall, CAI, RJC Power Plate, 3.5" THDP, DMH electric cutout, home built 3" mandrel bent exhaust w/ spintech muffler, Translator Plus, 3.5" MAF, q-boost controller, Walbro GSS340M, hotwire kit, 60#injectors, and 275 60 15 ET Street Radials out back.
On the way- Powerstroke(mounted, but needs plumbing ran), and Alky. (hopefully ported heads before too long)
13.035 @ 102.28 on stock turbo and ic on pump gas w/ 1.77 60 ft. | 
