You should post a picture on the bike for a better “gauge” of your aerodynamics.
I’m a bit shorter and also “chunky” (180 cm, 85 kg race weight) and I squeezed 36 km/h out of 230 watts, but the course was completely flat (like 40 m elevation change over the 70.3) and with just 2 switchbacks. Also, did it on a TT bike in an average position and had an aerojacket on the back wheel.
We also have similar running paces. My 70.3 run split was 1:41. Two weeks later I ran a 19:23 open 5k and 2 months later a 40:51 open 10k (both PBs).