pushrod length/measuring question

hi,i,m buildind a 451 stroker low deck,the bottom end is complete and i,m up to buying the pushrods,the engine is using a comp cams hydraulic ex 285 hl,its using the hughes 1.5 rocker system,ok so do i just buy standard oem 383/400 pushrods or do i need set up and measure,i have a adjustable pushrod checker which i purchased,can someone give me advice on all this?????