Roadmaster bikes were produced as the in-house brand by CWC/AMF in the fifties, Hiawatha was a brand sold by the Gambles retail chain and some of their bicycle line was produced by CWC/AMF but other suppliers were also used.
If you have one of the CWC/AMF sourced models then it can be dated with reasonable accuracy by the serial number combined with specific frame features. The bicycles CWC/AMF produced for retail clients were based on the Roadmaster line and the sheet metal will physically interchange between the models based on the same frames. In some cases, specific sheet metal was produced exclusively for the Roadmaster or retailers lines so while it will fit across lines it may not be brand correct when mixed and matched.
Post pictures of what you have along with a serial number and I can probably answer your questions more directly.
