The plastic nose cone is 8 3/8" exposed. The fin can is 2.5" tall.
For everything to add up to the overall length of 19.5", I cut some 35mm tubing to 8 5/8" long.
If you know your Quest kits, you may have noticed my motor mount tube isn't yellow, it's white. BT-20 is a little thicker and much stronger than the yellow Quest motor mount tube. It fits these orange plastic centering rings and slides into Quest 20mm tubing perfectly.
To fit the fin can, I cut the BT-20 motor mount tube to just under 2.7" long. That's a little shorter than a regular 2.75" long motor mount tube.
Take a look at the forward centering ring. It's a pretty amazing design from G. Harry Stine when he did the rocket design work for MPC in the early 1970s.
That middle forward extending ring fits inside the motor mount tube and acts as a engine block. The square tab at the bottom ends up over the engine hook preventing it from coming out of it's slot.
At the top I drilled a small hole for the Kevlar cord.
The original instructions have you tie the Kevlar to a hole in the fin can shoulder. I was concerned that would bulge and raise the body tube where the Kevlar was tied. By tying it around the top of the mount and out the drilled hole, I avoided this potential problem altogether.
Here's the finished mount - Notice the Kevlar going around the bottom of the upper centering ring.
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