I have my 4.2 torn down and the head has more corrosion that I am comfortable with in the water jackets. I started looking for a replacement head and I ended up buying 3 of them.
The challenge is none of them are off a 4.2 E type but the list is as follows
3.8 E type head that has had some performance work done such as polishing, believe new seats and stems, additional oil holes drilled in the bottom valley of the cam trays, and the water jackets machined out so they are one large slot in lieu of two small slots.
2.4 head from a MK2. Does not seem to be a straight port. And not sure it would be a good fit.
4.2 head from a 420. This Head is bone stock.