I reckon you should graft a new skin full of louvres into that tailgate, you can buy the skins already punched out (don't ask me how much), like
this one from a Chevy S10...
...or I guess some metal fab place should be able to do 'em custom for you if you can find someone 'old school' enough?
Yeah as you've discovered, most cars are not built symmetrically, but the reason the cylinder heads aren't level is that they're interchangeable left to right, and the pistons can't be in line with the opposite bank because the connecting rods need to sit side by side on the crank journal.
It kind of surprises me though that whoever built those manifolds didn't account for the difference and make one pipe slightly longer than the other? I think that would annoy me and I'd have to fix it, but seems a shame to have to re-weld such pretty pipes!
Then again that's just me, I have to have everything symmetrical or I'm not happy, if I was doing twin turbos I think I'd have to import a pair of mirror-image turbos just so everything looked 'right', but I think
Nelson Race Engines are the only people that make 'em?
When I used to build speedway cars back in the day, there were two schools of thought when it came to bar work. You could either build everything so it crumpled easily but was independent from the other bar work, so if one bit got bent it didn't bend anything else, or you could brace the **** out of everything so the car was built like a tank, that way the bar work was so strong that any impact pushed the car sideways rather than bending anything, but the second option did tend to turn out to be a bloody heavy car!
Andrew