I think as Dan y points suggests below, the loading on the davits is uneven and actually will be more than 1/2 of simply the dingy and engine. You have to take into account i) other gear, ii) water that may end-up in the dingy from rain or waves, iii) dynamic loads from wind, waves, and even, backing into a dock (now and then). The description of securing the boat with "spring lines" is important to avoid the davits experiencing troque or wracking.

I'm not sure how the manufacturer came-up with the 175# capacity; but your planned loading is pretty much a minimum for any set of davits. So, if you have a decent set of davits, and a backing plate, and you're reasonably careful...