[DanEC]

Is one of your timing lights a dial back unit? Those are the handiest to have. I'm not familiar with the 351 series engine family but probably somewhere between 35 and 37 degrees combined initial and mechanical timing - all in at somewhere between 2500 to 3000 rpm. I would set the dial back light at 36 degrees and rev the motor until the timing is all advanced and steady and turn the distributor until you are reading 0 deg on the timing marks. That will leave you at 36 degrees total (no vacuum advance in this) and should get you relatively close.

Not sure what distributor you have or how adjustable the centrifugal curve is. If adjustable I would try setting it for somewhere around 20 crank degrees mechanical advance. That will leave you with initial timing around 15 to 17 degrees. Of course if your engine has a pretty big cam it may still be pretty lumpy. That's why I like to use vacuum advance to give it another 8 or 9 degrees of timing at idle to smooth it out a little (usually takes an adjustable vacuum can). Others like to go without vacuum advance, limit the mechanical advance and use more initial advance which is just another way to go.