Cap rate should be around 6% - 6.5% so NOI = 580,000 * 0.065 = 37,700
My OE budget is approximately 35% of gross effective income (incl utilities, based on build-up budget) so expected gross revenue is
= 37,700 / (1-0.35)
= 58,000
Apply vacancy rate of 5% = 58,000*1.05 = 60,900
Monthly gross rent = 60,900 / 12 = $5,075
So: $2,538 per unit for duplex
Or $1,692 per unit triplex
Or $1,269 per unit fourplex
Or $846 per unit sixplex
If those rents are within market possibilities it is worth pursuing otherwise I wouldn't bother.