[knomadd]

You're using a 3" block between the trans and cross member? That's HUGE! How high is your engine sitting in the frame? Maybe you need shorter engine stands to drop the whole assembly. I know you're running extreme drop members, so you may not be able to drop your engine and trans. If that's the case, you might have to run a completely new trans/driveline tunnel through the cab. I've seen this done with body dropped trucks.

As for the 6l80/6l90's, I believe they are the same dimensions externally, so it won't make much difference in your floor clearance. You've already cut more than I did. I was able to put it in with a high hump. Another member on here has a 6l80 that he put in with a slightly massaged low hump, but we're both using factory frame and cross members.

I assume you have a truck or van engine/trans combo in there if you have a 6l90. You might need to swap your oil pan and possibly trans pan for more clearance so you can lower the combo in the frame. It appears you're only options at this point are to drop your engine/trans combo or make a new floor section. I might not be seeing something that may give you a third option though. Good luck!