Hiya may,
There are some definite considerations to mull over when doing this conversion.
The 1500 case will have smaller oil passages (8mm) than a 1600 case (10mm). Then too, a later 1600 case will be of the dual relief style which is quite desireable in building a performance engine. This is NOT to say that a 1500 case cannot or should not be used, just that there may be advantages in using a 1600.
You might want to consider changing the oil cooler and the fanshroud cooling system. The doghouse with its offset oil cooler, introduced with dual ports in 1971, is a much better cooling system and, IMHO, absolutely necessary for a performance engine.