Don;
I don't know if Bolthoff is still around but he sure built us some fine ZL1 BBC engines back in the day. We had two- one in the car and another as a spare or being rebuilt by Geaorge at his shop Engine Systems Development. Consistent, reliable, and lots of torque. One dyno'ed at 665 hp and the other one at 666 hp. He ran without hearing protection, as we all did in those days so he couldn't hear very well at all. Now I have a bit of that same problem, too.
Although I haven't posted much lately in the Build Diary, I've been busy revising the Mirage rear chassis so that the suspension pick up points are located better. Lots of cutting & grinding & welding.
BTW, a salesman in a local abrasives distributor gave me a sample 4 1/2" sanding disk for my angle grinder; it is a new abrasive from 3M. I forget the name but that "32+" disk cuts steel like nothing I've ever seen. I was so impressed that I went back and bought a few 60+ and 80+ disks. If you do any fabrication, I recommend trying them.
I think the Manta Mirage should have good aerodynamics since it was based on a McLaren M8 but their conversion of that body style into a closed-cockpit coupe should have even lower drag than the original M8.
Regards, Neil Tucson, AZ