Coasted thru the timing traps after everything went quiet at 150 mph to find this (see attached). Well, being on an every expense spared budget, I reached out and borrowed a set of heads, stockers, from a "no kill shelter" for used motorcycle parts. You can still smell the questionable/criminal past. Nothing special, just cheap (free) and available.
Edit 1). Cheap (free) and available sounds like one of my ex's. She said she was "fast". I thought "racer". Nope, she just drank alot and put out on the first date.
Edit 2). Trying to make old parts go fast is about as hard as making fast parts get old so I always opt for the least expensive parts. YMMV.