After getting one of my "grail" watches last year, a 1972 Omega Flightmaster 911 pilot's watch, I recently found myself completely in love with Seiko's 6139-7100 "Darth Vader" helmet chronograph. Obsessed, I have to have one.
Picked one up, circa 1976 and decided to compare the sizes and cases of the two.
You can't compare the functionality, because the Flightmaster is loaded with complications, adjustable GMT, bezel, as well as full chrono functions with second hand subdial, 30 minute and 12 hour subdials.
The Seiko only has chrono with a 30 minute subdial (no second hand subdial), but it does have day/date.
Omega: 42mm x 52mm tall. Counting crystal and caseback, the 911 is 15mm thick
Seiko: 40mm x 48mm tall. Counting crystal and caseback, the 6139 is 13mm thick.
Weight. Hard for me to gauge because I have a heavy Omega mesh on my 911, but a much lighter hollow-link fishbone Z050S (had to have one of these -also used on the Bullhead) on my Seiko.
Arrived at these figures a couple ways - pretty accurate, I think.
Omega: 3.4 oz (with bracelet, total 5.6)
Seiko 2.5 oz (with bracelet, total 4.2)
Bottom line. I'm a big fan of 70s era watches- cushion cases in particular. This case style is probably my overall favorite. Bracelets appear integrated because the case partially covers the end pieces (especially with that "helmet" curve). Hope this gives a perspective you hadn't seen before.
They both do, especially concidering the age. I certainly can see why you love the design. Pretty massive watches for the era 
