I had the same problem on N/A BHG repair, the problem is after dismantling most of the top half of the engine you suspect everything.I spent days scratching my head (no wonder I'm loosing my hair) It turned out to be the distributor positioning, I had no problems with Turbo cam sensor after re build, but the N/A was very sensitive to positioning. Try turning the engine over and ask someone to rotate the distributors, if you get a puff of black smoke from the exhaust then you are nearly there. Also make sure # 1 piston was at top dead centre when you inserted the distributor. The piston should be at the top of its stroke and the crank pulley at zero.