Most of the folks on this forum will tell you that you should go to PTVupgrade for support, since you used their software to make your image. Having mentioned that disclaimer, I'll see if I can point you in the right direction.
First, I like the Instant Cake CD and its a good way to get a known-good software install running on your TiVo. Know that Instant Cake is pretty much just MFStools with an installer script.
You mentioned a TCD240 series-2 which is good, since it is software hackable. For your software version (v4.0.1b on the Instant Cake CD) you'll need a 4.0.1a kernel (which is actually a Linux 2.4.18 kernel -- you'll need to know that for any advanced network drivers you may wish to add). The so-called 4.0.1a kernel is killhdinitrd-able, and perfectly usable with the v4.0.1b TiVo software.
You can get a pre-killhdinitrd'ed 4.0.1a kernel off the PTVupgrade LBA48 boot disc (It was $5 last I checked). It also has several Series-1 and other Series-2 kernels (e.g. 3.1.1c and 3.1.5). You mentioned you already had a few modded kernels, so you will want to use the 4.0.1a one on your TiVo box.
Of course, you'll still need to copy it (dd) to your /dev/hda6 (or hdc6 depending on how you plugged in the TiVo drive into your computer).
Add the following lines near the end of your TiVo's /etc/rc.d/rc.sysinit file:
tnlited 23 /bin/bash -login &
BE EXTREMELY CAREFUL EDITING RC.SYSINIT. Any screwups and you TiVo likely won't boot. Also be sure to use the bootpage tool to fix the bootpage. Since you say your TiVO drive is in your PC on hdc, your command should look somehting like this (note the capital "P"):
bootpage -P "root=/dev/hda7 dsscon=true console=2,115200 upgradesoftware=false" -C /dev/hdc
That should get you going. If it doesn't work the first time, well... welcome to the club.