Aggregating Inputs

This question may very well likely be addressed somewhere else so please just point me in the right direction if that's the case. I would like to assess the impacts of visitor spending associated with a certain event. The data that I have available are not disaggregated to the level of IMPLAN sectors. For example, I have total restaurant spending, which is not broken down by Full-Service (501), Limited Service (502), and Other (Implan 503). My initial thought is that I should calculate the share of each component that contributes to the total (e.g. 501 is 26% of 501+502+503) and share out total spending to each IMPLAN sector. Is this the right approach? Is there an easier way? Many thanks!