Chuck, I pull my 12ft alum boat with 10hp motor with my Ranger bumper ball. I can push it up the driveway and in to the garage pretty easy. I don't think you will have any problem at all pulling it with the bumper on your full size pick up. If you think the motor will drag, tilt it up and put a piece of wood under it. Bungee the motor to the trailer and go fishing. I have pulled my rig to Cedar Creek and Joe Pool from Arlington. Hit Lake Arlington all the time.
I remember back in 1975 my Dad bought a Ford F250 xcab Camper Special. He had a 10' cab over camper and we took the old steel step bumper and cut off the hangers and welded channel iron to the frame and bumper slid inside of the frame channels so when the camper wasn't on the truck the bumper could retract to stock position and when the camper was on extended to 2'. I also welded out of 4" angle iron 2 pieces offset for a step as well as to hitch the 1971 16' Chrysler Bassrunner boat to. Now it wasn't dot approved but you could have lifted that truck up by the trailer ball and shook it and the truck may fall apart but the hitch and bumper would still be there. As nose heavy as that boat was yea I'd say your safe with it as long as you don't exceed the bumper rating.
The one you ordered have an adjustable drop? Depends on the ramp sometimes a pitch up say a 4" or 5" drop is easier to load and unload not to mention how it pulls. A 7" drop sounds radical to me for a first adjustment. To low sometimes is just as bad or worse than to high.