I can guarantee you there was no 350 Chev Sandman made. There were hardly any 350 HQ's outside of Statesman in 1974, and even then most were XW8 Kingswood sedans (GTS350 4 door). There were 2 x 350 powered HQ commercials: the Sandman concept vehicle (the Ewe't) and another built 2 months later. These were both 1972 HQ Kingswood utes. And all 1974 powered HQ's were TH400, there were no manuals.

XX7 is just an option code. Sandman became XU3 mid HJ, prior to that XU3 was neutral headlining in HG and HQ. There is nothing that cool about XX7 really. It is no different to XU1, A9X (we all know these). HQ SS was XV2. HQ GTS sedan was XV4 (359 version was XW8). B06 is Ambulance. XY7 is a dressed up 1-tonner. XX8 is a HJ Deville done up as a Isuzu for the Japanese market. Also note that XX7 really means SPORTS UTILITY or SPORTS COMMERCIAL, it doesn't just mean Sandman. There were XX7 option coded vehicles that were not Sandmans.