That seems reasonable, for sure. Maindeck Plague Engineers alone would be very powerful. If Smallpox gets cut with a focus on spot removal then there is less reason to go deep into Ensnaring Bridge, but you would be more susceptible to top-decks. When your draw engine is a 4-drop it makes it a little dicey, depending on the matchup, but especially against Delver decks. I think it's generally better to play Smallpox, some spot removal, and Bridge. You want more removal/locks then they have threats, then it's just a matter of who wins the disruption war (counterspells vs discard) to see what sticks. The good news is that Pox has been historically good against Delver decks because of the absurd resource denial. Uro and Oko are big problems though. Smallpox strains their resources so well but Bridge is weak to Oko.

Also, if you're playing Bitterblossom you could also include some number of Cabal Therapy. I don't see Bitterblossom as bad in a Bridge deck either; I think Bitterblossom is one of the best underplayed cards in Legacy.