Giant OverDrive road fork replacement I've got a Giant Revolt with a OverDrive tapered steerer (1 1/8-inch top to 1 1/4-inch bottom), and am thinking about replacing the fork with a shock.

If I used a shock with a 1 1/8-inch non-tapered steerer, can I just replace the bottom bearing? 

Or can I add a tapered spacer and convert the straight steerer to OverDrive? Has anyone tried this?
You will need a crown race reducer.

1-1/2" -> 1-1/8" is a pretty common size. The 1-1/4" -> 1-1/8" that you are looking for is rarer but it probably exists. Maybe the de-evolution from Chris King.

If you can find that part, the existing bearing can stay.

Also do some research on the Problem Solvers headtube reducer; you would just use the bottom piece. If you use this, you can use the existing crown race (and bearing obviously).