2040, 2045, 2050, 2054, and 2055 all share a similar modular design; everything above the crank centerline is in one die-casting, with a bolted on bearing cap/bottom. This assembly then mounts into the pressure-cast plastic tank/chassis. The vibration isolation is all in the handle mounting at the rear of the tank and up along the right side.
Poulans were a little different: the plastic tank/chassis <b>was</b> the bottom 1/2 of the motor, and at least some of them came without plated cylinder bores. Expectation was Harvey Homeowner wouldn't ever get enough hours out of it to wear it out anyway. 2050 or 2150 would probably do a dozen years of firewood for a midwestern fireplace. Poulan might do 1/4 that.
2150 is different; the same as Husky 350. Plastic case 1/2's split sideways, use same jug as H351, old Jonsered 2149. 2149/351 has been replaced by slightly larger 353/2152 with enough more cc's to put it within stones's throw of 026/260 peformance.