Knoebels built Twister in house as well. That just means they hired the carpenders and followed the construction as they wanted everything done. Twister was designed by a local person. As for Six Flags I could see them just designing coasters for their own parks since they are so big.
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Parks hit for 2000!
PKD,BGW,Knoebels,DP,HP,PKI,HW,SFKK,SFA, Camden, SFO,CP,WL,IW,KW,BP