I think that is totally fine. Just state your assumptions and say something like:
The conjunction of these positions are hold by XXX (papers' names). It is compelling since.... it is beyond the scope of the paper to do justice on defending these claims, for some defenses, see... (names of papers that provide a detailed defense).
I think Glasperlenspieler's advice about considering the connection between these assumptions and your argument is really worth of consideration. But bear in mind that you can still argue for a conditional thesis that if X is the case, then Y is the case, which is still helpful to the debate on the table in a certain way. Just clarify in which way this thesis is important to the debate. Then you are good.