You don't even need a new oscillator. I really need to write the method up more carefully, but for what it is worth :maybe a new oscillator?
New Awesome and Easy Way to Bump a Wombat to 40MHz
I've found a new way to overclock Wombats. If you have a 33MHz Q650 or a Q800... Step 1 - bridge J29 with solder, it is next to the CPU. That's it. Your Wombat will now boot at 40MHz. The machine photographed above has a 16.6MHz clock fitted at G3! More detail. So it turns out that the...
68kmla.org
In short - a blob of solder will get a 33MHz Q650 to run at 40MHz, and if you want it more reliable (using correct 40MHz timings) a little bit more work is needed to give you two jumpers that let you select the speed and ROM timings. Note I think someone on that thread corrected which way round I said the settings were for two speeds - they're right, I was looking at old notes when I wrote my post and didn't have a machine in front of me.