Lawn Boy 30" Rider

[Dougryan]

Hi all,
I have the mower deck from a LB 30" rear engine rider that I plan to use as a tow behind mower.
It came with the spindle, blade, and pulley. It's an 8" diameter pulley with a 1/2" drive belt.

My plan is to power the deck with a repurposed pressure washer motor. B&S 875 series (6.5hp).
I need to take it all apart and measure, but I believe the motor has a 7/8" crank shaft with 2 keyways.

My question... How fast should the 30" spin? In other words, what size pulley should I get for the motor crank shaft?
I tried finding lawn boy part details to see the size of the stock drive pulley, but the mower is so old all of the parts are obsolete and I can't find the detail I'm looking for.

Thanks in advance,
Doug

Here is the pulley on the deck spindle.

 

[Richard001]

Here from the internet, a tip speed calculator:

Tip Speed Calculator - Calculator Academy

Enter the diameter and RPM of the impeller into the calculator to determine the tip speed.

calculator.academy

Entering the blade diameter of 30inches and the suggested tip speed of 19000 fpm gives this:
Tip Speed Calculator

Enter any 2 values to calculate the missing variable

Diameter 30 Inches (in)

RPM (Revolutions Per Minute)

2419.16

Tip Speed 19000

Richard