Diy PA speakers out of old car speakers

The overall dimensions of the box look OK for a 'disco' speaker.

I must ask again - are your car speakers definitely 8" (200 mm) as you 'thought' they were, and not 6.5" (165 mm)?

Whichever overall diameter the speakers have, do make sure the smaller circular cut outs to house the drivers have the correct diameter.
 
That 18" driver looks like a serious candidate given that its specs include a real world power rating of 750 W RMS (1500 W MAX) and the T/S parameters required to design a suitable enclosure.

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P.S. RMS equates to the continuous power I mentioned earlier, and MAX equates to the peak power.
 
Building a box is not a problem. And 2 new things that i found about speakers is that they are Zomax speaker and on a forum they say that Martin Wisman sounds bad but that was in 2009 and btw here is link to that thread Link it is in serbian but it is only place where i found somting about tham.