I'd go for a Minolta Autopak-8 D10 camera system. Not as well known as the Canons and Nikons but the flagship Minolta Super 8mm camera and built like a TANK!
The aspect ratio of a film camera does not change unless you matte it or modify the internal mechanism, BUT you can letterbox the image on transfer as long as you compose for same aspect ratio in the viewfinder when you shoot.
The native aspect ratio of Super 8mm is 1.58:1, so you'd have to lose some off the top and bottom to hit the 16:9 aspect ration of HD. Just mask it off in the transfer.
"The camera is a base instrument; you must do violence to it..." Orson Welles