Internal or External Balance?

[bordin34]

I am building a 440 and need a harmonic balancer and none of them say if they are for internally or externally balanced engines. I have a '76 cast crank and LY rods. From what I have read it was originally externally balanced. I do not have the original balancer. Could I buy a balancer made for internally balanced engines and add a weight to the flex plate or something like that.

[tricky lugnuts]

I guess you could do that if you were willing to have the whole assembly properly balanced, but I'd guess that it would be cheaper and/or easier to go with the correct damper/balancer for the cast crank. 

Looks like Summit sells external balancers for 440 engines with cast cranks. (Kind of pricey at $440 so you might be able to find a better deal, but . . .)

http://www.summitracing.com/parts/ATI-918601E/