Unfortunately, there is not any reference schematic with values on either datasheet for both parts that you have mentioned. However, there is a reference schematic with values on the DC/DC Designer tool for the MPQ8633B.
Yes, looks like the MPQ8643 has similar specs and the same package type, so they should be interchangeable for your application. Since you are deferring to the MPQ8833B for simulation purposes, then using the DC/DC Designer tool is a solid choice in judging the performance of the MPQ8643 in this case because of the similarity of these parts.
Note the only difference between the MPQ8643 and the MPQ8633B in terms of external connections would be the C_OL capacitor between the FB and RGND pins in this case, so these minor differences with this part in your model should be accounted for.
However, if you are still going to use the MPQ8643, I would see the differences between the simulations for the MPQ8633B if you truly want an accurate simulation for the sake of having a sanity check. But these differences should be minimal.
Hope this helps,
~ Krishan