Yep, I would box it, and just as importantly, add some crossmembers to take the twist out of it. Those frames are made to twist like a pretzel by design, and that isn't what you want in 2014 on our modern roads.
I'm running a model a frame under my 27 and am putting 424 HP through it, but I boxed it and added not only crossmembers behind the motor, but I used a Speedway engine crossmember so that everything is supported well. This one has been on the road for over 25 years like this with no issues.