I got a 77/78 axle in there now it just maybe gets to the far plunger.
They used 20 mm so that your stock wheel would fit. .
I dont think anyone was using 1 in or 25mm , back when these frames were built.
Here is what happened last axle I bought sv 650 front forks. Found one in Canada , with shipping ran around 30 bux. Fronts have a stepped thicker portion. . Unbeknownst to me the SV used two diameters over different years... of course I did not know and the one I got was smaller. So I made a sleeve on an unfamiliar lathe, and flubbed it., a bit under size , gave to make another... aaarrrgghhhh.
I learned in the shop years, easiest is to get ground shafting, then thread both ends.. or 1 end and weld a nut on the other.