The Tundra oil filter threaded fitting is a 3/4"-16 without a doubt. I am considering relocating my filter also. I took a new Toyota oil filter, YZZB5, down to the local bolt and fastener store and a 3/4"-16 bolt fits perfectly.
PermaCool makes a universal kit for relocating the filter and here it is:
http://www.permacool.com/Catalog/Cat_page27.html Their catalog also contains specific parts to build your own depending on where you want the inlet ports pointed. Here is the big catalog:
http://www.permacool.com/Catalog/Contents.html
Summit Racing has the PermaCool universal remote filter kit for $34.95 here:
http://store.summitracing.com/defaul...3D12%26s%3D172
Mounting the remote filter in the vertical position underneath the battery looks like a good spot. Having the filter in the vertical orientation allows you to fill the new filter with oil prior to installing it to minimize the amount of time the engine is running with no oil supply after an oil change. Using the custom remote filter brackets from PermaCool with inlet ports to the side looks like the best option for a clean installation.