Alas the trouble here is that "iPod classic" is not enough of an identifier.
The sources I have indicate as follows:
If you started with a 6th, 80 GB (the "thin 6th"), that should be the 1.1.2 firmware. It maxes out at 128 GiB. (This is because it only supports 28 bits of logical block address.) There is no way to change this (without running Rockbox,that is).
If you started with a 6th, 160 GB ("thick 6th", or sometimes "6.5"), that should be the 2437 board with 2.0.1 firmware. It *may* handle the 240 GB drive. I don't know if this has been tested or not. "Tarkan", who builds CompactFlash and mSATA adapters for iPods, reports that it will not support a CompactFlash or mSATA adapter with >128 GiB. Apparently it can tell the difference and sticks to 28-bit LBA with anything but an actual hard drive.
(Conflicting info: I do have a "thick 6th", came with 160GB, that has firmware 1.1.2. I dunno.)
If you started with what is commonly called a 7th gen, but which Apple calls a "6th late 2009" or some such, you have a 2437 logic board with 2.0.4 or .5 firmware. It should handle the 240GB drive - or a CF or mSATA adapter with more than that. CF cards are very expensive in larger sizes, mSATA "drives" are much more reasonable, but they use a lot of power and get accordingly warm.
(Before going further I would put the old drive back in, hook the iPod up to iTunes, and see which firmware version it has.)
Ordinarily I would recommend the CF or mSATA solution for rugged use like yours. But since you already have the drive I would just get the replacement 2437 logic board. Be sure to get the one with the 2.0.4 or later firmware for compatibility with later changes to SSD. Since no more hard drives are likely to be made in this form factor, 240GB is likely the max capacity we'll ever see; expansion beyond that will require some form of SSD.
If you do decide you don't want the 240GB you can probably resell it on eBay for a decent price.