340 stock manifold where can I put temp sensor?

You could drill a NPT hole in the timing cover water port. The covers are cheap enough that if you brick one you can just get another. single planes, dual planes. Probably a wash on functionality on a TBI. The atomization of an injector is much better that that of a carb. The multiple turns the dual plane offers can cause the fuel to 'fall out' of suspension but thats only during very low speed operation and even then its debateable that its any worse than a carbs performance (at nasty atomization idle) or an older Mopar TBI setups. Thats where intake heat works. single planes were the choice of MPFI as the injectors had a nice place to mount at the end of each runner that was on the same plane. Air-gap models have this ability as a dual plane.
Maybe this one would fit? Not sure what values the Holley are (most likely GM) but it could be an option. I read that the Holley ones are not that accurate anyway.
AEM 30-2012 - Temperature Sending Unit, Electric, 1/8 in NPT