roseda...
four options...
Install a flush tension head solid rivet in the flush shear head countersink... then carefully mill-off the excess-head-height flush. May specify a reduced bucked-tail to match the reduced head after milling.
Install a protruding tension head rivet with the manufactured head on the non-flush side... and then drive the tail into the countersink. Mill-off the excess bucked-tail height flush-to-slightly high.
CAUTION: These two options may require the shop to develop techniques to accomplish work successfully [shear testing may be required].
Install 718 Inconel flush shear head Hi-Lok pins and A286 collars... or may install A286 or Inconel [silver-plated] hex/2X-hex nuts to a relatively low [shear-rated] torque.
For smaller diameters, flush shear head Inconel blind rivets are available [1200F rated].
NOTE: there are Huck and JO-Bolt style flush shear-head A286 blind-bolts [commercial P/Ns] available... but I am not sure of the max temperature rating.
CAUTION: all rivets or pin fasteners should be unplated... whereas all mating nuts/collars should have silver-plating.
Regards, Wil Taylor