It would be fairly easy to do that, but the result would depend on the chosen variables and conditions, which may not be the same as those used in the past.
A while ago, we published a study on the impact of various political funding reforms from 2004 to 2014—there were several during that period—including the system of quarterly allowances you are referring to. We also analyzed the consequences of those changes on the party's finances. All that is available on our website.