Not sure exactly what you mean by "bolt up right". If you mean "bolt-in", it definitely won't be that. Basically, you will be building a 65-66 GS clone on a 68 platform, and you will need some fairly scarce parts to put this combination together. At the very least, you will need the 65-66 GS engine mount frame brackets and rubber mounts for sure, and possibly the GS exhaust manifolds also.
What kind of transmission do you want to run? If automatic, you will need a 64-66 nailhead TH400 or a 65-66 nailhead ST300. Anything else will require a rather expensive adaptor plate. For a manual, you will have to find a GS bellhousing. Big car bellhousings won't work unless you do some serious cobbling on the clutch linkage. No matter which transmission you pick, a 64-66 engine will make for an easier swap. However, a 57-63 engine can be made to work if you are willing to do some mods on the crank and flywheel/flexplate.
Besides the above, be prepared to put in a good bit of work on the exhaust, wiring, piping, and linkage. It would be a big help if you can find someone who has built a GS clone, even though yours will have some differences because of the car year.
Good luck on this, and please let us know what you decide to do.