I would stick with the original motor if it is? I have a blue 253 quady re tuned and jetted with a very mild cam and timming set back to hq standards, on the dyno its putting out a very healthy 139kw a rear wheels with little work and minimal cost. a vn 5.0 fuel injected is only good for 165kw at the fly wheel and 142kw for vs v6 so bugger all difference and you have got to love the sound of a carby motor sound compared to fuel injected.