Welcome to CHR!

Sounds like you’ve already started to eliminate some of the obvious “easy” things, i.e. new plugs gapped correctly (.035 for standard ignition, .045 for HEI), new wires, set the timing 8-10 degrees with vacuum advance plugged and look for total timing of 32-35 degrees.

I think you also have touched on what the root problem(s) might be. The 750 is in all likelihood too big for a 350. If the cam “sounds radical, it’s probably too big as well and perhaps has a trashed lobe (or several bad lobes?). You’re probably going to have to open this one up to really fix. Good news is the 350 is a great platform for a rebuild. If it hasn’t been bored, a .030 over with some good pistons will work well with your Vortecs however; with the compression being 190 all the way around, I’d be tempted to select a more appropriate cam, new lifters and timing set and put things back together. The Performer RPM is a good manifold and I’d go for a 600 Edelbrock 1406. Select a cam that performs well with your overall combination considering your rearend ratio, transmission type, and c/r your piston/head combination provides. Remember too that cam break-in for non-roller cams is critical and the cam manufacturer’s instructions must be followed exactly or your new cam may be trashed in the first few minutes of run time.

Give us a bit more info and we’ll chime in with more suggestions. Techinspector1 is a whiz and if you ask nicely, he will probably help you with a dyno simulation as well as point you toward multiple helps/articles to determine the compression ratio numbers and how to accurately calculate what you’ve really got going on inside the engine.

Again – Welcome and stay active – we’ll sure try and help you out!
Glenn