z31 to s30 blues

You can make it work but you'll need extensive knowledge in car work. The other alternative is to pay someone but that would cost you a lot of money. I see a couple of options. First one is like you said, to fix the rust. This option would probably be the best since doing a swap to a S30 is going to be a major pain in the ass and the suspension components won't really work so you'll end up losing out. Also frame rot can be a bad thing but it's very repairable as long as you have the money and a shop that can do a good job. I bet you anything it will be easier and cheaper to fix the frame rails than to buy a S30 do a swap and fix it up to be equivalent to what your 300zx is now. Now your second best option would be to sell off the 300zx altogether or part it out. Use the money you get from that and start all over again with a S30. It would be much easier and cheaper to use a 280zx turbo engine as it bolts up with no problem. As far as performance goes you'll find that running 12's with the S30 shouldn't be any harder than doing it with your 300zx and it may be cheaper too. On the other hand a 300zx with that much power compared to a S30 with equal power the 300zx will handle much better at high speeds due to better areodynamics. It's up to you but if it were me I'd probably start finding a very good shop to get an esstimate and then go from there. I would forget about the idea of swapping over. It would be much easier to just start over with the S30 than to swap it over. In short it can be done but it will take a lot of work and thats just for the engine. For the suspension and such it will take even more fabing to make work. Good luck