[kwmech]

You should not have to replace the flexplate. I'm pretty sure I didn't when I did my swap. You will only use 3 of the torque convertor bolts anyways. I do remember having to replace the starter and bolts though. Transmission lines are up for grabs depending on what year the 4L80 you have is. I got an early one where it had both cooler lines in about the same place as the 700r4 and is the same as the 400 also. The later model 4L80s had a front and a rear line. If you have the later one where one of the lines goes to the back of the trans case, yeah they are quite different with the fittings and will have to be adapted to the radiator. Cross member will have to be moved back and possible re-drilling of the frame may be necessary. T-case shifter rod will have to be lengthened as well as the brace that bolts to the side of the case. I think I used the bell housing dust cover braces over without modification. The 4L80 should have both tone rings in the transmission, you just have to purchase another sensor and can plug into that with the stand alone harness and not use the sensor on the T-case. This is a good time to take the T-case apart, inspect, reseal and maybe a good time to put a slip yoke eliminator kit in the case. I mounted my controller in my glove box on the side with the peel and stick velcro cut to fit kit. My modifications were more involved as my 'burb had a 700r4 that I replaced. For your filler tube and gauge I would look for a matching used pair. I don't know what happens to these at the wrecking yards---they just vanish never to be seen again, just like the 1 sock that goes missing