How close to 2 is your almost 2 year old? The Pinnacle has a 2 year age minimum requirement.
With a large almost 2 year old, I would do everything I can to keep my baby rear facing as long as possible, for sure until age two, but longer if I could. There are many seats on the market that will not only allow him to continue to rear face now, but should get him a decent way beyond his 2nd birthday, some more, some less than what you'd pay for a Pinnacle. The Pinnacle is a wonderful seat, for later. I personally prefer the Frontier, for space reasons, if you do get a seat that will keep him rear facing longer but need a high weight, tall, forward facing seat before he is booster.
If open to suggestions on rear facing seats that would work, please post back and let us know. If you want to keep it within a certain budget please include that info as well. Also, still wondering what month his birthday is, since I've seen "almost x age" mean anywhere from next week to 6 months from now.