You probably won't get the exact same axle, wasn't Dexter that they used back then. Was a company now called AlKO that made the axles. Dexter can provide you with the axle you need.
Unless you are confident in your ability to get all of the dimensions 100% correct I would let a shop that does trailers and trailer axles do the measuring, and order the part, and probably have them install it too. They measure wrong they eat the cost you measure wrong you now own Dexter axle that won't fit.
It is possible to determine the original ride height of your
scamp, the arm going from axle to tire has the square shaft coming through it. Originally the square would have one set of points running parallel to the frame. Like this <>.
With a wheel off so you can see the square shaft you can jack the camper up until the shaft is again lined up with two points in a straight line parallel to the frame. Measure the distance from the wheel spindle to the ground. New axle needs to have the same height for that spindle.
The old ones had the arms for the wheel going forward rather than toward the back, most trailers today do trailing not leading. So the axle has to be turned around.
The brackets are not centered on the axle of the
Scamp so that bracket measurement has to be requested for the order AND has to be reversed when ordering because you will have to turn your Dexter around to have the wheels in front of axle rather than behind.
Essentially the axle bar goes across the frame tucked in pretty close to where the rear dining floor goes up. It has a weld that is to that rise in the frame and a longer one along the frame.
Some people have frame members added to run a more common trailing axle, or do that work themselves.
Order
brakes, you won't ever regret having trailer
brakes and they can't really be added after without spending a lot more money than they are being added when ordered.
New wheels are 5 bolt, the old wheels are 4 bolt. You can get 4 bolt but I suggest not doing so, especially with brakes. Since almost no trailers with 4 bolt use brakes parts will seldom be in stock if you have a breakdown.
Pretty easy to make a modification to support a 5 bolt spare tire on the back instead of a 4 bolt. Just an adapter that bolts to the original two bolts and has a support coming down and welded to the back bumper.
If you have any questions that don't get answered by someone feel free to send me a PM and I'll try to answer them that way. But a lot of people have done this and there is more than one way to skin this cat. You will probably really like how much smoother it tows and how much less the contents get thrown around with a new axle.