Howard:
My old, fat body sympathizes with you. (Let's not subject PB members to a visual comparison!)
After watching my Dad (60+ and 50 lbs overweight at the time) jump 5 foot gaps from the top of one 6"x6" post to the next 20 feet up in the air, I have respect for what old, fat bodies can accomplish when determined and/or foolish. (That was the first time a ever REALLY yelled at him and made it stick.)
Once the beams (2 each side) were up, I'd put planking across them temporarily to work on, moving it out a 2"x4" at a time. Form nailing it in place, if needed, for stability or sanity.
How deep is the water past the end of the dock?
Good luck and be careful.