Who are you calling old? LOL Ironically I was just chatting with Chuckles last week about some irrigation issues he was having.
Aluminum heads these days would be pretty easy, and you guys are in the right ballpark. Quite ironically I was just speaking with another "old-timer" a couple of weeks ago about something pretty similar along these lines...... In 2007 or so I started designing a new 7.3 PSD head - 4 valves per cylinder and CR injection. That design is roughly 80-90% of the way there and has been at that stage since about 2009/2010 - which is the last time I touched it. I discussed the merits of bringing the design up to today's modeling standards and potentially finishing it and open-sourcing it. Not sure if I will or not - the basic premise still involves a ton of work in the real world. It still needs a dual/triple CP3 front cover design, would need new pistons, custom length pushrods are easy. I went ahead and designed/utilized as many existing and off the shelf components as possible - although most of them are not originally found in anything with a blue oval on it.
I stopped simply because the costs were going to get out of hand.... but that was a decade ago and most of the components now are readily accessible, and since 3D printed sand casting has gone mainstream it is pretty cost-effective for low production parts and one-off castings. I get things cast in direct 3D printed sand on a pretty regular basis now.
No matter what - I'm not going to make any decisions or do any work on it until the current 7.3 project in my shop is finished for a friend and out the door and he is happy.