Check/clean/repair/replace grounds (a failing ground can cause long cranks due to shonky sensor signals.)
Check/replace Crankshaft Position Sensor.
I'd put my money on the grounds first, tho. There are, I think, four that should get your main attention:
1) Ground strap from engine block to firewall (both ends)
2) Ground connection from battery to chassis at fender liner
3) Ground connection from battery to engine block at dipstick bracket (near distributor)
Clean chassis parts down to bare metal (small patch - about the size of a postage stamp - will do) and apply corrosion inhibitor on reassembly.
Also, check the make sure the braided ground strap between the engine and firewall isn't itself dirty - this can cause "signal drain," and give you all sorts of headaches. It's OK to replace this with a proper cable - I do it all the time (the braid is cheap, and bad to use. But, it's cheap.)