Originally Posted by stefanj

That is indeed a rare find!

Was it the version with the hand-written instruction set?

I have at least one adaptor for putting 18mm motors in 21mm FSI mounts. Might be expensive to ship, but if you really want it, lemme know.

All FSI motors are super rare now. Especially the A4 /B4 / C4/ D4. I'd consider hanging on to any you find and selling them to a collector. Buy a bunch of Estes B4-2 to fly that Viking on!