Why did the DC-3 have a much higher cruise speed than the HP.42, despite their similar weight and power?
Struts every which way, uncowled engines, wheels with fenders hanging out, wires, bits sticking out here, bits sticking out there, corrugated skins, fabric wings and tail... it's a mess; a flying Truss Bridge.  There's just too much to try to quantify it like that.

You could probably take a DC-3 and start adding all those things one at a time, and each item would knock off 10-20 kt, and eventually you'd end up down at 87 kt, but the slower you get the smaller each accumulative penalty would be.