Kodak recommends starting with at least 100ml of XTOL stock for each film but the replenishment rate is only 70ml per film (I don’t understand why these numbers would be different – but may be someone else might be able to).
Therefore it seems reasonable enough to assume you only need 70ml of chemistry to process one film
With a 660ml bottle capacity it would seem you have 2 choices:-
1) Use 350 ml (5 x 70ml) of XTol + 310ml of water (not quite 1+1)
2) Use 330ml of XTol + 330ml of Water & use marginally less dev than Kodak recommend
Either way the numbers are not too far outside the normal operating range to be at least in with a chance of succeeding
Either way you are going to have to run some tests to see what Dev + Water + Time works for you