that is a drop in box. alternatively, you could build one for less but it's more work unless you are familiar with working on them. V3's are easy so ya, I would build one personally.
as long as your inner barrel comes close to the threading on your outer barrel/silencer, I wouldn't worry about BB's hitting. since you want to use a TB and a better hopup sleeve you'll be getting the BB's to go a straight as it can. all you need to worry about is any IB wobble in the outer barrel. easy enough to shim with a bit of tape.
wrap rounds of tape on the end of the TB inner until it doesn't move inside the outer.