Hello questions on a 1995 camaro z28. Ive rebuilt the engine myself and am around the 420 fwhp mark. Due to this im upgrading the 4L60E trans and putting a 2800 stall torque converter in. Ive bought a trans alread specifically for the 1993-1996 4L60E and the torque converter. Im doing the swap myself. Questions i have are as follows:

The manual says to mark the alignment of the flexplate and the torque converter that way i can realign when i put them back together. Problem is im putting a new torque converter in so i wont be able to make this mark. I was wondering was the mark due to balancing of the complete unit i dont know much about this department.

Next question is when i replace the trans they say that it will probably bring up some codes just wondering if there is anything special i have to do besides plugging it up to the harnesss etc and making all connections i figure i will have to do some tuning.

Well probably ignorant questions but im pretty ignorant on this area. Ive been reading and cannot find out much information on this topic so i hope someone can help me out with this.