If it is still serving its purpose now, and its too f'd, I would save until you can do the full build how you want it. From experience I've learned that doing a little bit now and then more later is only going to cost more....a lot more usually.

If the engine is still good, possibly consider pulling it, selling it, and dumping the cash straight into your new build. Yea, you'll be without for a while, but it might help you get to the end sooner.

 

I looked heavily into both options before I did my engine build. I looked at a 2JZ swap and an LS. I ended up building my motor. My build was eagle rods, weisco pistons, got the block decked and honed, new valve springs and retainers, racing studs, comic gaskets and a couple other smaller pieces. On top of that I am full bolt ons with a dyno tune. The car makes 310 hp naturally aspirated. I built mine to be procharged so I kept the stock compression. The funny thing is that before I built it the car ran low 14 seconds in a quarter mile, after I built it and made more power the quickest I ran was a 15.1 but we blame the tune. All in all the engine build cost me $8,500 but I was deployed when it was being done so you could save a lot in labor. If I were to do it again I may have just manned up and done the 2JZ swap. I love the built motor but it's a little frustrating the numbers we get out of it. I would say if you want more than 500-600 HP I would swap it. Just my 2 cents though.