For non manoeuvring flight, if you take moments about the CG datum (or any other convenient longitudinal station), consider the weight at wherever the CG is, and lift to be acting at quarter chord, then the tailplane load to be acting at quarter chord of the tailplane - a bit of quick algebra will drop an answer out.
It won't be exact, because of the pitching moment effects of the mainplane and the lift on the fuselage, but the answer should be within 10% or so of the truth, which will give you a fair idea.
For working data, you just need a 3-view of the aeroplane, and a W&CG report. If you haven't got a suitable W&CG report, rumour has it that the example aeroplane used for the CAA/JAR ATPL exams is a B734 so you can create a reasonable approximation from that.
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