State of aggregation of "ate" complexes
The crystal structure of lithium tetraethylaluminate has been published (DOI)
and as far as I can tell from the abstract, there is no indication for a dimeric anion here. It might be save to assume that the balanced equation therefore can be written as:

$\ce{2 LiCH2CH3 + Al2(CH2CH3)6 -&gt; 2 Al(CH2CH3)4^{\delta-}\,Li^{\delta+}}$