Lexus 4lt is no doubt the best bang for buck. For our Harrison we bought a crown front cut. With front cut you get to start and run the engine(cool) and you also get full working engine wiring loom. Plus lots of other things you can use, we even used the aluminium radiator out of it. And things like air conditioning compressor, power steering pump you don't need are worth money to sell.
We even sold the TV out of it.
And then you can grab some 2nd hand turbo's off Skyline/300ZX etc(twin factory turbos are large enough for 4lt engine), find a nice 2nd hand intercooler, do some pipe work and you have 50%+ more horsepower.
Well maybe you need some larger injectors(we used Supra ones) and maybe an aftermarket ECU as well, but...it will still run smooth like a factory EFI engine. Or if you want it to look cool, go for bolt-on 8 stack injection setup
And if you wear it out or blow it up. At worst you can buy another bare engine for $1000 and drop it in. You've got all accessories.
Then you can also go Chev LS1 path. It also has it's advantages, well 1 main advantage, it's got cubes.
With Harrison you can also bolt in a Skyline independent LSD GTR rear-end(or Ford 9" etc), bolt on some of the killer Skyline brakes. This is what we did and you have a Cobra good enough to win at the nationals for a really cheap price. We proved that last year.
And our normally aspirated Lexus Harrison does 12.4 1/4 mile on street rubber. Don't need big dollars anymore to have performance.
Or you can go Classic Revival and use a nice Ford XR8 rear end...LS1...yum.
Or you can go DRB and choose from old trusty chassis or new jag chassis...more DRB's around than anything else. Sounds like they will even be going to Japan...cool.
Or you can ... sorry just too many options to list.