you may be on to something . I pulled two choice MS marked spring perches and both had the the tack weld. They don't appear to ever been rebuilt or needing rebuilt from their condition of metal etc. Of course they could have but i don't think so. I also have a NOS aprox 50 Year old (from style of paper sticker tag) MS spring perch that does not have a tack weld.
Knowing the one spring perch (saddle) of my example wasn't ever restored till earlier this week and now re-doing the other bushing I replaced 20 years ago, (seeing evidence of the spot weld snapped off in the metal), I feel safe to say there should be many more MS coil spring perches or spring saddles out there with the tack welds or signs of having been tack welded prior to bushing replacement. Sure, this tack welding procedure could have been a select time frame only, but I feel confident it was done to original examples built in the same time period of my example (11/2/66).
FWIW, since the reproduction replacement bushings I have been able to locate ARE NOT the same as the original bushings,
I'll not be tack welding them again. . My example will not ever be in any Thoroughbred Class and since the detail is obviously not well known or understood at this time, it makes little sense. Besides that, rubber sleeves welded into any suspension part is simply not a wise choice in my opinion...unless the bore is loose and no other replacement arm (or perch) is available, then...and only then, perhaps welding them in is an option.
Now if I wanted a "truly restored" pair of "MS spring saddles (perches) for my build date, a pair of "MS" saddles with the straight-tube bushings tack welded in, would be in my opinion 100% correct. By straight-tube bushings, I mean like what I pictured earlier ((and now again below) in this thread, ones without the "stop flange" on the one end, as it appears all replacements I have located to date have on them. (I have found NO replacement bushing shafts that are same or similar to what I found as original)