You can do just on the leopard 2. After i reduce a little on a side to put the treads of modernarmor (the only that i want to keep) as i made a composition of units from Leopard2 I reshaped the turret, from modernarmor i reshaped the body and introduced the sides of leopard1... but i'm setting up the uv to use only the one of leopard2...

and i have to modify the wheels cause the original has only six.
The image is the work in progress... but i don't like the texture i use... it's only to test of what i'm doing with the uv
and it looks too much brilliant.