Leonard Adams did the build on the Twister at Knoebels, under the supervision of Dick himself. Leonard does have his own company, doing retracking, rebuilding, and such, but this was his first big project.
The fact that the Knoebels have a lumber yard on site - well I do not know what kind of lumber they sell, but they do have lots of carpenters.
And somebody had to work that crazy lift hill scheme. Leonard now has ads in trade magazines, so maybe he will get some more work.
And technically, Kennywood is capable of doing all of that, since they did the Thunderbolt in house in 67-68. Just a lot of labor involved nowadays.