Centerbolt heads refer to anything 1986 and later. They could be TBI heads
- old heads, 12 intake bolt holes, all are same-angled.
- TBI heads, 12 intake bolt holes, center four are at a different angle
- Vortec heads, 8 intake bolt holes, straight down angle.
- All heads starting in mid-86 became centerbolt valve covers.
Of those, you can swap TBI stuff with the older style but you have to wallow out the holes to match whatever angle you want.
Vortec heads are only cast in numbers that end with 062 and 906. Those two heads (what are referred to as Vortec heads despite the "vortec" name being used for 15 years) have the different ports and 8-bolt pattern. They are not interchangable. Period. You could make them work with about $1500 worth of welding, machine work, and modifications...