opinions on a head swap

4V swap... since you already have all the stuff may as well rebuild the engine as well so you get a nice powerful and reliable package. Consider buying an aluminum block to save some weight and a set of cams for those 4V heads too

oneturboneeded...do you have all the other stuff needed for a 4V swap? Knock sensors? Coolant crossover tube? Wire harness? ECU? If you're gonna get a different block and build the Cobra motor from the ground up then it's probably gonna take some time to get all the parts and do it right. So you might as well get a set of NPI heads for dirt cheap, throw them on, and drive your car while you're planning/building the Cobra conversion.