In case other folks are considering this conversion, I would recommend sticking with the A-Data 40x for now. I've converted my iPod video. The A-Data worked fine without compiling a custom firmware and bootloader. The Transcend 133x pitches an error upon boot:
rockbox boot loader
version: 2.0
ipod version: 0xffffffff
ata: -80
no partition found
The iPod firmware works fine. I've also tried to compile a custom firmware and bootloader for the iPod, but no dice - same error.
Stick with the A-Data! It's for sale on newegg.com for about $80,-. If you wait a couple of months, you will probably get it for $60,-. Speed is no issue. The player is very responsive. Data transfers are slow to and from the player, but 'Hey' big deal.
Cheers.