what grade of metric bolt should be used for suspension parts or to secure lift blocks. Hi grades I commonly see are 8.8 and 10.9. Don't know if that suffices or if you need higher.

Metric class 8.8 is the equivalent to grade 5 and class 10.9 is the equivalent of grade 8. Class 10.9 will be more than enough overkill for your needs.

I could only get 8.8 in the length I needed, this would be for plates that hold the radius rods and tranny x-member. 8.8 good enough?

That's perfect.

 

Harder bolts are actually more brittle, and will break rather than bend. Also they'll be more likely to rip threads out of the body nuts.

 

8.8 is as hard as you want. Better to bend, than break.

That's what I want to hear! thanks