Um, I apologize for the smart remark answer... Using math is the correct way, changing the value of a modern film resistor is almost impossible.
The thought come to mind, as a boy I had a beat-up Tripplett meter that had a pop up dual meter housing. When changing the battery, the circuits were exposed, a 2 watt (big) carbon dog-bone resistor was trimmed to tolerance with a large notch in its center, painted the color of the 3d place "dot"...
That image remained in my mind when a resistor was needed that I could not double up. So I filed one to fit.
To our readers, any resistor that has changed value should be removed, there in no telling how much more it has changed, if it will change with heat/cool or be noisy...
Yah, I have to get back into my Zenith 53, I relied on those old resistors. They were initially fine, then after a few hours of operation, they have changed value and change when ever the radio warms up and the radio looses sensitivity. It a good radio for about 10 minutes
A project when I get "caught-up"...
I got a bargain on 1% 2 watt metal film resistors so I can hit the OEM values. I intend to paint over them so they will "agree" with the Zenith markings... They are as big as the 1/2 watt resistors in the radio... So they will look and reach the existing terminals
Chas