theres a few different brands out there, this one with dual kenwood 4" is decent & says it uses factory mounting, but doesnt say if they are 4 or 8-10ohm, most likely they are 4ohm. could probably email for confirmation. they arent a true 2 way with separate tweeter, just one way with a "whizzer cone" but for the limited freq range of a small front speaker they should sound pretty good.
https://www.firebirdcentral.com/1970...r_p/das-93.htm
heres a single cone dual voice coil version with dual tweeters for stereo sound & uses the stock bracket. & a few other versions listed below it.
https://www.classiccarstereos.com/19...html?rrec=true
& before these were available what guys did was to gut a stock 4x10 & use the frame to install dual 4" or 3.5" speakers of your choice, but for the price of the cheaper ones available its probably easier to use one of them or could even swap out the cheap speakers for better ones & just use the plate...
https://www.rickscamaros.com/custom-...yABEgIES_D_BwE