For 1960s and 1970s Mopars (and American cars in general) what do you consider to be a "big" V-8 engine.
I would say anything over about 375-cubic-inches to be a big engine (going by cu.-in., not external size).
I consider engines like the Mopar 383, Chevy 396 and Ford 390 to be big. Of course, along with the even bigger engines like Mopar 400, 413, 426, 440; Chevy 400, 409, 427, 454; Ford 400, 406, 427, 428, 429, 460 and 462.
A Mopar 361 I would classify as a medium sized V-8.
Small Mopar V-8s 273, 318 and 340, although 340 may be medium-sized, especially considering the power they make.