Your 250 should have hydraulic lifters and the tappets shouldn't make any noise at all...
I would have to check my shop manual, but I believe the correct valve adjustment is "one turn beyond zero-lash".
I have a '72 C-10 with a 250 (unknown vintage). I've never been able to get the timing quite right, but my original Mono-jet carb and "Transmission-Controlled Spark" were removed and replaced with a mid-'60s Rochester BV carb. I installed a rebuilt distributor for s '67 Chevy last year; that helped a bit.
I have trouble with the points closing-up and burning; the rubbing block on the contact arm seems to keep wearing down. (These are the points that came with the rebuilt dizzy (A-1 Cardone); I'm going to try a set of Blue Streak Lubri-points next tune-up)
What carb are your running on your '67 ?
Also what plugs and plug gap? Too wide a gap can cause missing at high speeds...
I had the head rebuilt at 96,000 miles; truck now has 119,000 miles on it. Head's great - now the rings and bearings are shot !
