those slant six engines were long lasting did not always start and stalled a lot but they were durable... I think it was on a 70 impala 350 in the early 70's dad used sears spectrum 10w40 later we used pennzoil that car was sludged up so bad when we rebuilt the engine at 60,000 miles we had to use our haands to scoop the sludge out we did from the camshaft up and that car ran for another 200,000 miles.. i dont know if the sludge was because the car was used and they never took care of it or it was something else like the oil