Unless you / owner really want to find 50 year old iron heads and recondition them, I would also consider the AFR heads as a quick and very good alternative.
Just for fun I put Tokyo Japan into Summit's delivery address and a pair of AFR heads would be $191 UPS expedited shipping.......!! Plus your import duties.
(be careful which model AFR head you pick, they are a great head for SBF but some are more suited to competition use and you don't need to go too wild on valve size etc).
There is a good and easy to read article on AFR heads, although it's a later engine it's still a 302 and they use a better inlet manifold ( I have a Holley Performer RPM - ported- on my race Mustang as we have to use dual plane and it revs to 7,500 easily, they are $200 plus cost for tuner to port - not a hard job).
(I can't seem to post a hyperlink for some reason)
Or Google "AFR Heads Hot Rod Magazine SBF" and it should be top article. They "bolted on" 100+ bhp and said it was best they'd ever seen from just bolt on heads, no other changes. And this is the AFR Street head, not race. Torque also increase by more than 50 lb ft.
The Mangusta exhaust manifolds are not as good as some (cheap) alternatives but you will need to stay with them and they could knock back performance a little. The headers they use are pretty good for what they are, but even if the Mangusta headers knock 20-30 bhp off their number it's a strong little engine for just heads and little effort, no real tuning expertise needed.
I doubt you could rebuild your existing heads for $1,600 even if you didn't have to buy a new head.
PS I don't have any affiliation with any company mentioned above.