post an ad in the classifieds on this website, and ask for a set on the '73-79 forum. Also try Ebay and Craiglist. I don't have an extra set, and haven't been to any junkyards lately to look. But I can keep my eyes peeled, that's all I can offer. Good luck!
I assume you're putting the 300 in a '79 F150/Bronco? I used '79 F150 4x4 perches, with '79 motor mounts. Engine block was an '85, but I'm pretty sure the casting stayed the same except for the fuel pump slot when they went EFI.
Glad my posts are useful.
That's a 600cfm Holley, model 80457-1. In all honesty, I'm not the biggest fan of it. No matter what I do, the idle is very rich and even though it's supposed to be an emissions / economy oriented carb, it gets worse gas mileage than the generic dime-a-dozen 600cfm Holley 1850. I've tried the 1850 on both my Broncos and have got around 13 - 15mpg in town and 17 - 19mpg on the highway. I'm going to keep my eye out for another.