We've got the time to add some. To attack with 50 units we need 9 transports; we have 7 right now and one is already in play with The Council. The other six are in Unshackled; they just arrived this turn. Unshackled is building a transport, it will complete this turn. That gives us 7 to load up on Turn 240.
Debt-Free and Ellis Island are making Destroyers that we could switch to Transports on Turn 240 and rush. Weltonspolt is still cranking out Transports but it is too far away to rush and use this next turn. Rush and use for reinforcements, yes, but that doesn't help with initial landing.
We have 3 Mech Infantry already in Production. All three will complete on Turn 141. We have several Modern Armor that we could switch to Mech Infantry next turn and, if needed, rush for Turn 141.
In a nutshell, it will take us two turns to have 9 Transports to invade Saber. In that time we will also build (naturally == no rushing) 3 Mech Infantry.
Of course, we can change those Mechs to SAMs. We can build more Mech Infantry and SAMs. SAMs first, then the Mechs, to blunt Saber's air force.