Welcome to FEBO from the desert! Please post some pictures when you get a chance. Recently when I got my 64 Imperial, the first thing I bought to fire it up was a brand new battery! The advice others have given you is very sound! These guys are pretty awesome on this site!!
Was thinking about this today. Did you happen to check the 360 block and see if someone added any block filler to the lower water jacket area? A common thing to do along with the O-ring cylinders and machined rocker shaft posts. That would push it more towards a race only combo and not a street...
I would say you need at the very least a 850 CFM Thermoquad. Or a 950 CFM Holley, although I really don't care for leaky Holley's. But to each his own.
Also, if running a flat tappet (non-roller) camshaft make sure you have either an oil with lots of zinc and phosphate or and additive like ZPPD. The additive is much less than new lifters and a camshaft!
There is a difference. See the Year One link below.
https://www.yearone.com/Catalog/challenger.cuda/electrical/road-lights-.-barracuda/brackets-_-hardware
Recently there was a post on FCBO regarding the correct color of turquoise paint. I ordered some from Mancini, who I consider a very top notch Mopar company. Then I compared that color to big block valve covers I have that I now are factory original and never repainted. My conclusion is that...
Uh oh! Sounds like you need a new Speedometer gauge! Regardless the issue, you're taking the dash back out! Sorry for the bad news. Take out and see what happens with the needle.
Try this link:
https://www.forebodiesonly.com/forum/threads/challenger-instrument-lights.30772/
Or this one:
https://www.forebodiesonly.com/forum/threads/led-bulb-conversion.25340/post-151866