The BUSA website does list the 60-class 2-stroke as the top end for 2 strokes and a 61 as the low end for 4-strokes. If you don't expect sport model performance but instead expect "scale-like" flying for example, needing to start with a shallow dive to be able to build speed for a loop, then either 70 4-stroke might do.

http://www.balsausa.com/store/product.php?id_product=44

BTW, I feel I need to take exception to the following sentence in the description: "Our model is accurate in outline, but has been modernized!" A comparison on the BUSA eindecker with three views of the EIII will immediately reveal this as false. Both the tail and the rudder have been enlarged and altered in shape, The wing has been moved back in the fuselage (which is too short and stocky for the EIIIand more like the EII) and the nose lengthened. The model gives a nice sort of rough impression of an EIII but it is absolutely not "accurate in outline."

It's a fun model and, by all accounts, a great flyer. But I'd prefer truthful descriptions on all model websites.