It's a very rare occurance for me to get a phone call from a potential customer where the build plan for the motor has a projected time frame spanning several years.

Usually, they want to know how much, and how soon can I have it?

I don't even try and stay abreast of who has, or where someone might find heads that are no longer produced, or what they cost.

If someone is interested in using head packages built around components that are no longer produced....... I let them do their own homework and price negotiating.

So, from my perspective, I only recommend parts that are "readily available" to anyone, and where there are reasonable quantities available.