There is a SST as per the FSM that attaches to the fuel rail in front. I think I have seen the part made by Actron but I am not 100% sure. I know Blue Point makes one. For some reason Toyota did not have a valve on the fuel rail to attach a gauge to. Go figure.
Try YT's search thread. A member" Life On A Board" tested his and provided pics.
That's what I was thinking. You'll need something that will get inline with the fuel line from the tank. Something with a banjo fitting combined with a longer, purpose made bolt to feed dual banjos might work. With the build you've got going, it might not be a bad idea to look into installing a guage. Maybe just a hard mount in the engine bay. I bet you could find something cheap that would just T into the fuel feed line the same way the URD 7th does.