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Kinda hard to tell in the pictures, but it does look like you have the head with the integral cast intake attached to it. If you can't unbolt the intake manifold from the head, then yes...you can't change the intake without getting a non-integral head.
This is a 250 6 I am working onSent from my iPhone using Tapatalk
You look to be in luck, I had to find another head that didn't have the intergral intake. I don't have any number or ideas on the performance increase as its waiting on exhaust pipes, don't want to burn a valve ruining it with just headers. Sent from my iPhone using Tapatalk