I had 425hp & 425lb ft on my old Harvey engine on a 4wd manifold no probs & had seen 432hp with it !

I'd go with Lloyd on the prediction of hp figures & when the manifold becomes restrictive. It is slightly less laggy than the 2wd item & the hair line crack shouldn't matter too much, they all do & it's inside, not all the way through !

Good luck

jb

p.s. I prefer the sound of Cossie's wit a 4wd manifold !