well, just by looking at my name you can tell im a ford fanatic, but truthfully they are both great engines. They both have innumerable aftermarket parts available for your needs. So, the 302 revs faster and can make a lot of power. The edelbrock performer package for this makes 291hp @5500 and 310lb-ft @4000. the 350 also has more torque, with the same system it makes 310hp and 375 torque. So, if you're looking for torque and have extra money to spend on the 350, especially for driving a heavy van, i would go for...i cant believe im saying this....the chevy.
....or you could go with a 351??? hahaha