In my I '66 I test fitted my TKO 600 with the 347 and it barely made it. Luckily I didn't have to do anything to the tunnel. It depends on who made your crossmember. I got mine from Dark Horse Performance.
I have the same from Dark Horse for a TKO and it does fit, but it does not have a good drive line angle. I spoke with him when I got it installed and he said yes that is how it will fit unless you mod the tunnel, or I guess someone mods the case on the gearbox. I moved it up as much as I could, but still bad drive line angles IMO. I have the older TKO (4 years old), not sure if the newer models are dimensionally different. The TKO is getting the ax back to a 4 speed as that is all I need and can use a better racing gear box. The TKO just does not bang gears as good as a top loader or T10 type of box without a bunch of work (again IMO).
Rather than leaning they would need to be lower I think. This is one of those things where you need to do the math. Do a trial fit if you can, measure the angles, check clearance and work out how much you would need to drop them and if it is possible.