electric radiator fan

i'm looking at changing the stock fan in my '99 Silverado Z71 4.3L V8 with a perma-cool cool-pack unit. i've found a great deal on a unit but it is for a
17x28.5" (part#: 19517) radiator core but i have a 19x34" (part#: 19516) core. i've seen several sites that say the 17x28.5" unit will work and i know the mounting holes are the same but i wanted to get some of your opinions and/or see if any of you have made this kind of application work. below is a link to perma-cool's website should you need a better description.
http://www.perma-cool.com/Catalog/Cat_page18-1.html
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whatever wrote:

(assuming yours is a NBS 99)
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