IMO #46 head cores are not worth $300. They'll need a lot of work to make performance heads out of 'em.
According to the online info I can find, they came mostly on '69 400 2-barrel engines, and have small valves & press-in studs. They also do not have hardened valve seats. So, about all they have going for 'em is small chambers, in case you need more compression.
But, it they have screw-in studs. that will increase their value. I assume it cost around $200 or so to have Pontiac heads converted from press-in to screw-in. Can also add seats & 2.11/1.77 SS valves. But, all that costs $$$. If you give $300 for the cores, then have everything done correctly, you could easily end up with well over $1000 in 'em.
If I was gonna put that much into some early heads, I'd go with #12, #13, #16, #48, #62, or #64. That way, you could always sell 'em to somebody doing a '68-'70 resto. Don't think there are many '69 400 2-barrel restos going on.
