You can use a hand-held tachometer or a Vibratach or a Sendec style tachometer.

Or if you have a rather fancy timing light that features a tachometer, you can use that.
Beware what I have been saying about crankshaft driven ignition systems and a wasted spark.
The spark rate of a Briggs is the same as for a two-cycle engine........one spark every time the piston comes up (which is one revolution of the crankshaft).

The tach I have is used for industrial type motors. I will be putting a piece of reflective tape on the flywheel and measuring off that. I assume the rpms should be flywheel revolutions per minute, correct?

flywheel RPM = crankshaft RPM

WOT should be around 3600 plus or minus

If you see RPMs far off 3600 then the conversion factor of your tach is wrong for that engine.

If you are using a strobe light tachometer, then the reading displayed will need no calculations, it will be a true reading.
The only thing you must keep in mind is that strobe light tachometers (the ones I have used) require that the user "dial in" the synchronizing control knob manually to manipulate the strobe flash frequency so the reflector dot appears to be stationary.
At that point (stationary or fixed) the RPM display should show the actual, true RPM.
But.........be sure that you begin the "dial in" process at a low setting because a synchronous moment (where the reflector seems to be stationary) will also be found at multiples of the same RPM. Meaning that a synchronous moment for say.......1,000 RPM is also present at 2,000 RPM AND 4,000 AND 8,000 RPM. While it is impossible to actually operate a Briggs engine at each of those example RPM (first 2 yes, third...maybe, fourth....no way), it is easy to "over dial" and have all of those RPM displayed on the tach.
Of course, you should be able to distinguish 1,000 RPM from 2,000 RPM pretty easily by ear only.