John...
I'm a bit confused by your question...are you looking for info. on the Gas version or Nitro version?
I have the original Seidel 7-70 ( Nitro %5 / % 6 Oil ) in a 1/4 / 80" Fleet biplane...I've never weighed it but in't in the 20 lb range.
I've had a few excellent flights on it with an OS carb.....plenty of power and cruising at 1/2 throttle.
Good luck with your Bulldog project.
Eric