Starting My 6-92s while the boat is beached.

If you don't have sea strainers just pull off the intake hose at the seacock, rig/make up some cheap pvc to go from your hose size to a garden hose fitting, make sure you have a shutoff valve right there for the garden hose, turn the hose on and then open the garden hose valve just a little to keep the impellor wet while someone else rolls them over as soon as the engine kicks open the valve to the garden hose full flow, then shut off the garden hose immediately before shutting the motor down. You should have enough water flow to run them up to at least 1000 rpms. I think it's a good idea to run them.

I can understand the desire to run the engines and see some benefit from doing so. However, I would be very careful feeding them with a garden hose. I can't see where you will get close to enough water volume from a garden hose. Even at low RPM or idle. I certainly wouldn't run them very long. Or, if you are planning on replacing the pump impellers anyway then maybe do this before then replace impellers after you run them.

A garden hose should supply 500 GPH of waterflow. It's fine to run them up to 1000 rpms for a set of 6-92's. It's plenty of flow, just keep an eye on temps. It shouldn't hurt the impellors, however sitting 2 years will, so might as well wait and change them anyways right before you launch the boat to use it.

I don't want to hijack this thread but 500 gph from a garden hose sounds awfully optimistic. Your suggesting 8.3 gals per minute. Maybe you have much greater water pressure in your neck of the woods but I know in most areas I've been you would be lucky to see 250 gph