First, 0.002" is a fairly large tolerance on a hole of that size. Honestly if you drill it it should be fine. Since the 0.142 OD that will be on the crank pin is not a standard ground stock size, you'll be turning that OD down on lathe. I'd suggest drilling the hole in the piston however you see fit. Then, leave an extra thou or two on the crank pin OD and use some files/sandpaper while it's spinning in the lathe, and keep testing until you get a good running fit in the piston hole.
Usually reamers are expensive, so you work to the sizes you have. If you wanted to retain the threaded stud/locknut configuration that the plan uses for the crank pin, you could: Take some 3/16 drill rod for the crank pin, then turn down the threaded part to the correct length and diameter, thread up to the shoulder. Then, the threaded part would be the right diameter, and also the part that actually needs a good fit is a standard size stock, so you could just go through the piston with a 3/16 reamer.
I'll also note that the tolerance on this hole is larger than usual for a reason: If the hole through your piston is slightly crooked (easy to do for beginners that didn't spot drill the hole properly), or maybe your piston bore isn't perfectly aligned, or maybe the pivot hole isn't perfect, etc, the crank pin - piston interface is the place where the engine will bind. Having a few extra thou of tolerance makes it easier for a beginner to get a running engine even if they made some mistakes along the way (didn't have their vise aligned right, etc). At high speeds this can make the engine a bit more noisy, but shouldn't be a problem.
So as a recap you can just drill it and make the pin to fit, or you can re-engineer the design a bit to use standard reamer sizes. Either one will work just fine.