What is a respectable 1/8th mile time

7.5 and you'll be doing very good. What are rearend gears?
Don't discount that 8 1/4. I beat the crap (with a 4-speed) out of a 8 1/4 with 355's and sold it to build a very stout 8 3/4 with brand new gears - bla bla bla - blew it up in 30 passes. That was my experience. built a dana 60 for less than the 8 3/4 and done.