keeping old php74 in poudriere

hello hackers@

I'm asking this here because of all the freebsd mailing lists, i'd guess
those in here would use poudriere a lot. Maybe the most.

basically i need to keep php74 and all the extensions for a machine
I have to look after. Would the correct approach be to use an overlay?
If this is the correct approach, do I need to:

1. make a ports tree that has php74 etc in it, such as 2202Q4, and then:

[a] remove the whole tree apart from the relevant ports
[b] as [a] but also remove things at the top level like Mk/*
[c] keep the whole 2022Q4 tree, and use that as the overlay.
[d] if [c] then how would the overlay be referenced? From the top of the 
tree, or does there need to be one overlay for each port?

2. not use an overlay but to use some other method?

tia,
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