On my 512 RB stroker with a Comp hydraulic roller and HS 1.6:1 rockers on 440 Source stealth heads, the pushrods I bought were just a bit short of 8.5".
Looking at my notes, I think 8.4750"? I used the Comp cams adjustable pushrod, with light checking springs on the valves. I used Smith Brothers 5/16", and fairly sure the 0.083" wall pushrods.
I came up with a range of pushrod lengths for between 0.020 and 0.040" lifter preload, and the minimum number of adjuster threads (where the pushrod / adjuster starts getting oil from the rocker), to about three turns down (any more and the oil to the adjuster starts getting cut off.)

Your measurements might be different. My block was cut to zero deck the pistons, and used a 0.040" Cometic MLS head gasket.