You don't need to be a shot blocker to be a rim defender. I mean KG's best in Boston was just 1.3 blocks a game and he was under 1 a number of years. Even the title team had Perkins at 1.5 and Garnett at 1.3 and only Pierce was even at 0.5 a game. Sure a great shot blocker is nice, but it is far from required. Heck look no further than Chicago. Noah is just over 2 a game and Gibson is pretty solid off the bench, but they aren't exactly swatting shots away like crazy people and their defense is off the chain.
With all of that said, Sullinger and Olynyk have to start given where this team is. They need to develop and the team needs to figure out what they have in them. Hopefully they develop and they become the 4/5 for years and years. Melo also needs to play 10-15 minutes a game to further his development.
Assuming full health this is what I would do with the current team
PG - Rondo 34, Bradley 14
SG - Bradley 20, Brooks 20, Crawford 8
SF - Green 35, Wallace 13
PF - Sullinger 20, Bass 20, Wallace 8
C - Olynyk 20, Melo 15, Bass 8, Iverson 5