If you had installed another speaker identical to the original that blew, you'd be back to where you wanted to be, I think. The information that's missing thru all this is...we have no idea what the sensitivity of the speakers are, and you've now introduced a new unknown...an 8 ohm speaker of a different mfgr, so the amp won't put out as much power, for one, and, no doubt it's sensitivity to a given power is the other. On speaker spec sheets, you'll usually find a sensitivity spec, that's made with 1 W applied, maybe on a large infinite baffle (large panel) or in a specified cabinet, measured 1 meter from the speaker, given as x-dB @ 1W/1M. Trying to find that info from our original speaker may be unavailable.
So, no real way to say what you'll end up with, deviating from the original. Is the original speaker still available? If not, you might check about getting it re-coned, if a like-original cone kit is available for it.