a VTOL needs to be able to create more thrust then its total mass. a quad is basically, always, running in the 'VTOL' format, so what ever mas the quad could be with the given power pack, your plane could be also.
There is more to VTOL: that just having enough thrust.
You need to consider stability. A quad uses very sensitive electronic gyro scopes to adjust the thrust of each motor to keep it level. It has no natural stability.
A plane on the other hand relies on it aerodynamic configuration so its forward motion keeps it stable. In VTOL mode it will have little or no forward motion so has no stability. You have to provide a system that gives it 'artificial' stability when it is in hover yet allows its natural aerodynamic stability to function when it is flying.
It is not easy to do!