mag thermostat housing?
Pretty sure you can use a pre-Mag thermostat housing. Sometime after 78? (not sure when) they changed the housing and only changed the construction when they released the Magnum motors. So technically an LA housing would work, just needs to be the later one.
I think I used
this one on my intake.
Here it is on my motor:
What are you planning to do with the single plane? Too bad it isnt drilled for the injectors.