Be wary of the scale bars, but the new data on Lewisuchus by Bittencourt et al. (2014) brings a fresh look to old Romer (1972) data. Here (Fig. 1) the scale of the posterior skull and tibia are pure guesswork until I hear back from the authors on my query.
Unfortunately the authors did not include basal archosaurs (Decuriasuchus and Pseudhesperosuchus) in their analysis, but restricted their taxon list to dinos and pre-dinos. Not surprisingly, Lewisuchus nested with Marasuchus. The large reptile tree nests Lewisuchus with Pseudhesperosuchus.
Bittencourt JS, Arcucci AB, Maricano CA and Langer MC 2014. Osteology of the Middle Triassic archosaur Lewisuchus admixtus Romer (Chañares Formation, Argentina) its inclusivity, and relationships amongst early dinosauromorphs. Journal of Systematic Palaeontology. Published online: 31 Mar 201. DOI:10.1080/14772019.2013.878758
Romer AS 1972. The Chañares (Argentina) Triassic reptile fauna; XIV, Lewisuchusadmixtus, gen. et sp. nov., a further thecodont from the Chañares beds. Breviora 390:1-13