Yup any 8XX bulb will work so yea a 893 would fit the difference between the bulbs are the length and light output.
I use a similar method now but have used this method in the past with great results..if you can get the basic wetsanding method down you can do wonders.
You can go the eBay route for a relay harness but I personally buy my stuff from http://www.theretrofitsource.com/