Here mine but is a 302 maybe it will help in rounting...
Pic of belt routing The belt lenght was 77.5in 775K6 was the part number at Advance Auto... To get ot on I had to uplug th elttle plug on he ALT, take out the top bolt and let the Alt slide over to get the belt on and pry the Alt back ove to bolt it back into place. But you having a 351 you might need a little longer belt. What sizes have you tired?? Also is your waterpump a reverse rotation??