Early Chop'd and channeled cars are not normally referred to as Street Rods. Street Rods are later OHV engined cars (usually SBC, but lately a lot of SBFs), Mustang II type front ends, that sort of thing. And a lot of billet aluminum, etc. To me it is fairly easy to tell the difference (at least in my own mind!
). In general pre-mid fifty's (or earlier to me) & post that era (think 60s and 70s).
Hard to beat a slammed 50s Merc, but I'm not much of a customs guy.