The sideoilers were 65 and later 427's only and bring oil to the mains first then moves on to the rest. Topoilers bring oil to the cam first then rockers and mains (and lifters if a hyd block) thus the topoiler. All FE engines other than the 427 sideoiler are topoilers. Even the early 427's are topoilers. There were also the marine 427 blocks that were cast as sideoilers but machined for topoiling. There is lots more but this is the basic idea. G.