Brightly suggests a rule for finding a truthmaker for any proposition p, viz., any entity t such that 't exists' entails p will do the job. Thus we have an 'equation' to solve. When p = 'Vallicella exists' a solution would appear to be t = Vallicella.
I'm not sure that will do. For a start, it suggests that every truthmaker T of a non-existential proposition is a truthmaker for at least two propositions, namely the non-existential one, and also the existential one 'T exists'. E.g. let T be the truthmaker for 'it is day'. Then it is the trutmaker for that, and also the truthmaker for 'T exists'.
Also, more worryingly, the entailment relation is very easy to satisfy. If p is true, then its truthmaker is any (existing) entity x whatsoever, since x exists, and p is true, i.e. if x = a then 'a exists' and p are both true, and we have entailment. Entailment only failing when the antecedent is true and the consequent false. (I think, I always get lost with entailment).