On our 1987 Turbo I used the inside belt mounting holes as well as the outside as you did. Why not use the inside mounting holes? Second question is what is behind the middle eye bolts? If there is just a washer or lock washer then I would worry about the eye bolts ripping through.
You mentioned that this is a DE car but in the San Diego PCA region there have been lots of auto-x and DE cars wrecked, probably as many as wheel to wheel racers....
Check this to see what might happen:
Car Crash Example