As far as I've seen AlterK is the only aftermarket company making tubular K frames for the FJM bodies. Additionally, it must be a specific FJM AlterK frame as you cannot adapt an A or B body unit to these very easily. All the primary mounting dimensions are different. The FJM cars are a bit of an anomaly as they are as wide as a B body, as heavy as a B body, but come in a wide variety of lengths despite being touted as a replacement for A bodies.