..... I got some brand-new YESTERtech(but very usable) pistons with no pins. WHERE is the best place to get some ? ....maybe lighter ones than the older OEM stuff. How much shorter can they be made without worry ?

Sealed Power may still list (heavy) pins for the older stuff.I have shortened them in the past to use with double truarcs.No problem but they were the old school heavyweight pins.I wouldn't shorten them for a pressed pin app.Just get some lightweight ones the stock length.Last couple sets I bought from Ross.

Isn't there better steel available NOW in the aftermarket ... than the OEM had way-back-when? This IS going to be a pressed-pin application.

Yes,I think Ross lists several different alloy pins that will work for you.

Is there any weight diff ?

You can shorten stock 1.09" ones 1/4" per side & still have plenty of contact area even for a race app as the contact area (piston/pin) is more than is safely needed (on a BB). Shorten pressed pins only of course. The aftermarket ones can weigh less as the ID is larger (length is the same) but using a better material the strength is not compromised. Shop time on the lathe is expensive so compare time/money for which'd b the better choice for you