Unfortunately the D70 (D2 series) saw the introduction of iTTL flash metering. In essence means you can ONLY use the SB600, SB200R and/or SB800 speedlites in TTL auto mode.
The camera uses a pre-flash to sort out flash output and none of the previous speedlites enabled the camera to perform this function. You should be able to use the SB26 in auto or manual modes but definitely not TTL. As you say, you have had some success but it was done to luck
You could also use some of the indepents 'guns (Sigma or Metz) but I couldn't tell you models.
PM me if you like with your phone number and maybe we can chat our way through the 'minefield' sometime. - HTH