You would need to buy from a metal supply CO, or Amazon.com, dont laugh, I got a piece of 6" round aluminum tubing .120 wall thickness & approx 40inches long for $23.00 shipped to my house. I thought it was a great deal.
People on Ebay sells titanium, aluminum, stainless,mild steel etc, I am sure if you search you could find a chunk of mild steel or stainless for a flange you need. That's if you cannot find a local metal supply Co.
I think the pistons that Tlowe sells will give you pretty high compression. A custom piston is going to run approx $100 per piston last I looked. For the pipe that attaches to the T4 flange,,,, you need to shape the pipe into the dimetions of the T4 flange.
Usually, your inline 250 block will not need to be lined honed. To check,install your crank bearings in the block & main caps,install your crank w/oil, torque, the main caps, & if the crank spins freely, your main cap line bore is straight.
