Why are there so many flycranks on the kit etch? I pondered this for a while, then remembered that Romford and Gibson wheels have slightly different crank throws. You need to chose your parts to suit the wheels on your loco.
Having worked out which set I needed, and there are several with two distinct designs, then it's a simple matter of juggling five layers of etch, lining up all the holes accurately, and running solder around the edges.
The result is, in my case, a pretty messy job, but cleaning things up doesn't take long with some abrasive.
The crank pin holes could be tapped and the pins screwed in place, but I just soldered them in position. At least that way they will stay put on the loco.