My 289 Performer intake from the 90’s had the rear coolant passage.
It caused issues for the shop installing/mounting the 65 kick down linkage.
I should have used a different shop....I was inexperienced at that time.
They welded a bracket to original bell crank...I was not happy about it.
It worked though...rant over.😁

I had to replace it back in 2009, the newer 289 Performer intake doesn’t have the rear coolant passage.

Both have 2121 part number.

I noticed back in 2009, I noticed Summit’s stage 1 = no passage, stage 2 = cooling passage

Figure additional cooling for racing.

Its common not to need that crossover.  SBCs had the same thing.  On high performance applications there is still no crossover, but the passages have taped holes, or can be drilled and tapped to run coolant circulation lines up to the front coolant crossover to reduce hot spots in the cooling system.  On a typical engine there's no reason to do this.  Interestingly the heads/intake on my 6.0 Diesel has the same situation.  I added circulation lines from the rear of the heads (drilled and tapped) to the t-stat housing (drilled and tapped) to ensure uniform cooling of all cylinders.  For point of reference though, that engine now makes more than twice it rated factory HP, and on a stock engine, or even one with just a tune these lines would be unnecessary.  There's debate they may be unnecessary even on my setup, but I didn't see the potential for harm so I added them.