Welcome aboard high schooler! The combo is nice.
I’m on board with the above replies. In the future, a little more compression and upgrading the heads will yield some really nice positive results since it seems this is all the engine lacks.
Your probably going to look for a 2500 stall converter and a “Trans-Go” shift kit is good to get.
Search the classifieds for the rear end. The 8-1/4 is by far cheaper and will hold the power no problem. I would look to a 3.55 ratio (min.) with 26 inch tires.
The 3.55 will work on the Hwy. fine.
To get this car off the line better would be a set of 3.91’s or 4.10’s. There a barrel of fun! But there not the very Hwy. friendly rpm wise.
