Hi VT22D!
Thank You for pointing out all of the subtle design changes between the 615 and the 616. I've never torn down a 615, so I don't know the differences that intimately. I learned some stuff today! I my case I was going putting a vacuum style pump on a latter 616, so it was easy. I just had to plug off the oil supply port on the block. I'm still running the 615 intake on my turbo 616 because it clears the turbo with no modification. I could have cut down the log style 617 intake and welded a cap over the end, but the 615 manifold was an easy, elegant solution. I hope the OP doesn't get discouraged. Most problems are solvable, it just a question of determination and money!
Cheers!
Chris

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1983 Turbocharged 240D
1982 Mazda RX-7
1974 Mazda Rotary Pickup Converted to an EV