The size of the Replace-A-Case isn't that much larger than the stock Dana 300 case. The shifter configuration is centered on the STaK 4x4 unit compared to the offset of the stock case.
As far as building a Dana 300 without a Dana 300? It can be done using the Replace-A-Case and all new heavy-duty aftermarket components like a 32-spline front-output shaft or a 32-spline rear-output shaft that uses a shorter tailhousing manufactured from billet aluminum (STaK offers these too). Also readily available for the Dana 300 are 4:1 Low gearsets as well as bearing rebuild kits. Of course, this isn't your only option. You can also assemble a Dana 300 using the Replace-A-Case and quality used components from an '81-'86 Dana 300 core. This will create a stout transfer-case assembly that can be upgraded over time as needs and funds dictate. Either way you slice it, new parts or old, the STaK 4x4 Replace-A-Case is an awesome upgrade to any Dana 300 transfer case and a great option for those eager to step up to a geardriven transfer case without the cost of purpose-built Low-geared units.
The split case design of the Replace-A-Case eliminates a need for the bottom inspection cover and also makes the installation of larger 4:1 gearsets much easier.
DANA 300 OVERVIEW
The Dana 300 transfer case uses all helically cut gears and a cast-iron case. It benefits from a compact size and its versatility in being able to mate up to a variety of transmissions. Available in '80-'86 Jeep CJ-5s and CJ-7s, two versions of the Dana 300 were produced: a reputedly stronger short version and a long version. The reasoning for the two versions is said to be due to the varying wheelbases of the CJ-5 and CJ-7, with the weak link in the long version found along the mainshaft. Both offer a 2.62:1 Low-gear ratio and use an aluminum tailhousing, a 1-1/4-inch intermediate shaft, and 23-spline input shaft. There's also a Scout Dana 300 that was used in the '80 International Scout II. A few differences exist between the Jeep and Scout models, but most importantly, they do not share the same bolt pattern. The Jeep 300 uses a round six-bolt pattern. The Scout 300 uses a four-bolt "Texas" pattern that is essentially the same pattern as the five-bolt Dana 20, making it an excellent swap candidate for early-CJ owners seeking a lower gear ratio.
With the front and rear case halves set side by side, we began assembly of the Replace-A-Case using the LoMax 4:1 gears and components from our existing Dana 300 T-case. All of the internal components are installed in the same manner as with a standard Dana 300 case. A standard Dana 300 bearing kit was also used. | 
The intermediate gearshaft was pressed into place in the rear case half. The front- and rear-output gears, clutch gears, and sleeves were also installed along with the new shift rods and shift forks. | 
The intermediate gear was then set in place on the intermediate shaft. Before joining the case halves, we turned the output shafts to ensure that the gears were meshing properly. |
STaK 4x4 supplies a length of rubber O-ring to seal up the case halves once joined. The O-ring seal fits in a machined groove around the inside edge of the front case half. The front output is also shown installed. | 
The case halves were then joined using the supplied 3/8-16 stainless steel socket-head cap screws. | 
The front-input support was installed on the Replace-A-Case. |
The new billet aluminum rear cover and the rear-output tailhousing were installed, as were the front and rear yokes and the STaK 4x4 universal-shifter assembly. | 
The front-output support was installed along with the yoke. | 
The STaK 4x4 universal-shifter assembly offers a good amount of adjustability to fit multiple applications. |