Snowman, I have found it best to buy tools and do things myself.
For that exhaust flange to manifold. Go to your local steel supplier. I know there has to be one. Get a piece of 3/8" flat steel and have it cut by them to the shape you want on a iron worker. With the plate. Buy a hole saw kit or just the size you need with the drive arbor. Drill it in the vice. Use a 1/2" drill and run it as slow as possible. You can even trim it with a round file.
This is the kind of stuff you will learn to do and use the skills for the rest of your life.
You really need to jig everything up on the motor in the bay. Expect to not drive your car for quite a while. Maybe jig on a spare motor and take lots of measurements.
I try to do as much as I can myself but any type of machine work would be impractical for me to do myself.
I bought the flange I need premade out of 3/8" steel
I'm going to put he 292 manifold in hopefully this weekend and then I can start doing all of that fitting and final fabrication. I'm sure you understand that I can't take my car out of commission for more than a few days. I guess that's the burden of working on your only car.
69 Buick Special Deluxe. Intercooled Turbo Chevy 250 @ 15psi on a stock long block. It's kinda fast.