The structure given here possibly only applies to the "jscr" variant, because I see quite different examples out there for "ascr". In particular, "ascr" files don't seem to contain a bplist at all!
AppleScriptHeader: {
0x0000: 4A 73 4F 73 61 44 41 53 31 2E 30 30 31 2E 30 30
- magic number?
- ASCII: "JsOsaDAS1.001.00"
}