I have two ford small block circle track engines in the shop and measured the thread depth. the ford motorsports block is 2.00 and the Dart is 1.75.I would think in your application I would set the block up in a mill and drill the shallow holes out to get the same engagement as the others.most aluminum blocks are counter bored approximately .250 from the deck so the load is below the sleeve flange.With the power level your after I don't think you would be successful running a shallow bolt engagement and if it didn't work out and the holes were drilled deeper after the bores were finished i think you would have a bore distortion problem from the deeper engagement.Bill