I've got a few drivers lying around that are screaming "use me"

Since the center channel of one of my HT systems now lacks a center speaker, I was thinking of building a box with two JBL 8" 2118s and a single JBL 034 tweeter.

My observation from a few other systems I have built/known is that the center channel audio material is mostly voices and, therefor, the center speaker does not need to go very low.

The "other" JBL components in this system include (2) 15" woofers, 1" compression drivers and slot tweeters, (2) studio monitors - 4312, (1) 18" woofer.

Are these JBL components suitable for a center channel speaker?

What frequency would be a good crossover point?