To stop the rust I would recommend POR-15 or an equivalent.
With this stuff you do not have to get all the way to bare metal. You just have to get all the loose stuff off, however I would guess the more that you can get off the better. I used a wire wheel on my angle grinder and went at it.
Here is a link to a post on POR-15 for you to read.
As for the clay, only thing I could recommend would be to use a pressure washer and maybe mix some all purpose cleaner in with it if your pressure washer allows chemicals to be mixed in with the water. goodluck

"4X4 in upper case is $X$" Quoted from http://4crawler.com/4Runner.shtml
'00 tacoma 4WD---Sold to Toyota
'93 pickup 2WD
'85 pickup 4WD