I can understand keeping the cost down but if you are gonna go V8 why a 305, not much of an upgrade from a 258 if you look at the numbers? To answer your question tho, they are both good T-cases, strong as hell and very reliable. You will have to adapt the Dana 300 to the SM 465. Unless you were planning on going with a 4:1 kit in the Dana 300 i would probably just stick with the NP 205. Also your driveshafts will mostly likely (99%) need to be changed, most likely lenghthened in the rear and shortened in the front.