Re: springer fork
Steerer tubes on forks are head tube length specific to a degree. The early cantilever frame bikes didn't come in a large range of sizes so that ht length was pretty consistent throughout the different manufacturers. They were all 1" however but there were some odd ball sizes in regards to head sets thrown in there of course.
These days with the large range of sizes available for modern bikes the headtube lengths are all over the map. Pretty much all are 1 1/8" now also. And most are also what they call threadless and the older ones are threaded.
So if you are trying to adapt one of the repro forks on an older style frame you should be ok with a minimum amount of fuss. But if you are looking to adapt to a more modern frame there could be issues.
"The future is already here, it is just not evenly distributed"