MAF and Speed density will both be down on power at altitude.
The MAF is using intake air to trim fuel mixture, and in most cases also uses the O2 sensor to verify the MAF is correct. Speed density uses the O2 sensor to trim the fuel mixture. Not as quick or accurate (EPA doesn't like it) but it does work to achieve the correct tabled AFR mixture ratio. A huge plus for the SD over MAF (in my mind) is you're not stuck with a butt ugly snorkel intake.
Carb will be down on the power as well but will run rich and will get richer the higher you go.
Power loss for MAF,SD and Carb are 3% for every 1000ft of elevation rise.
The Sniper that Bill has for sale is an example of a system that will serve you well and make your life simpler once installed. The horror stories of EFI tuning have largely subsided by and large in the last 5+ years. They are still are out there though, especially on 8-stack systems (not just Speedmaster) and folks who want to self-tune thru Heath-kit type installs.
Air density drops with altitude, your only real fix is boosted with forced induction.
https://www.garrettmotion.com/news/n...r-air-density/
https://www.enginelabs.com/engine-te...engine-tuning/
But back to your original question. The Edelbrock Pro-4 EFI is an excellent system. Sequential Port Injection VS Throttle Body Injection, and Edelbrock is also highly rated in Tech support staff that A:answer the phone and B:know what they're supporting. Their kit is complete, Intake manifold, Gaskets, Dizzy, Pump, ECU, Harness, Rails, Injectors
https://help.summitracing.com/app/an...-style-mean%3F