Well, I have some 1/40 Alpha models, and they are about the same as the super poseables. If the Toynami Alpha is truly 1/55 scale it will be shorter than the super poseables by an inch I would guess.
It's 13.7 meters tall in battloid, so bring that to 1/55 scale, that's how tall it should be.
I stole this from Robotech.com forums user GIR_Prototype...
VFA-6H (Blue Alpha)
Fighter Mode
Length: 10.25m
Height: 4.60m
Wingspan: 8.2m
Scale Length: .213541666667m=21.35cm=8.407in
Scale Height: .095833333333m=9.583cm=3.773in
Scale Wingspan: .170833333333m=17.083cm=6.725in
Guardian Mode
Length: 8.00m
Height: 5.72m
Width: 4.84m
Scale Length: .166666666667m=16.67cm=6.561in
Scale Height: .119166666667m=11.92cm=4.691in
Scale Width: .100833333333m=10.083cm=3.969in
Battloid Mode
Depth: 5.25m
Height: 8.75m
Breadth: 4.84m
Scale Depth: .109375m=10.937cm=4.306in
Scale Height: .182291666667m=18.229cm=7.176in
Scale Breadth: .100833333333m=10.083cm=3.969in