Stacking M.O.T. to create an E-E core
The described transformer seems to have the same cross sectional iron area as the original with twice the original window area and a bit less than twice the original magnetic flux path. The original primary winding should be appropriate. The level of saturation will be unchanged since that is determined by the voltage, number of turns, frequency and iron area.

The original primary winding will have pretty close to the same maximum current. It should run slightly cooler because there is more iron area to dissipate the heat, but the heat losses generated in the copper will be unchanged. Rewinding the primary with the same turns of a larger wire would allow more current. It would be difficult to calculate a new current rating, but a reasonable estimate could probably be calculated.

Tightly joining the two halves and keeping them joined may be  difficult.