For better drivability, replace M1 with Weiand from craigslist?

The way that engine is set up now, looking at the lack of choke and big single plane, makes me wonder how the idle quality is and what that cam is.

There are ways of using a mic and a solid lifter to check lobe lift x1.5 to get actual lift. You can also check duration from .050" lift on the crank, with a degree wheel on the harmonic balancer, or timing tape. It's best done with a piston stop to correct and find actual zero and mark it on the balancer, instead of trusting the mark as not being shifted from the rubber in the balancer.

Typically, lift x 1.5 will give you an idea of it's range, as cams get bigger in lift, they usually follow with duration and overlap, giving you some idea of RPM range that it's intended for.

I'd start by popping a valve cover, pulling a rocker shaft and at least checking the cam lift, with the pushrod and hydraulic lifter unloaded, with a mic and magnetic base.

You can put a piece of wood with a channel in it or something like angle steel under the pushrod to help guide the pushrod, like a pool cue, to help keep the correct pushrod angle. It won't work with the rockers in place, because the spring pressure from the valves will compress the hydraulic lifters.

Just be sure that the mic is at the same angle as the pushrod and you can get pretty darn close to actual lobe lift measured. It would only require pulling a valve cover.

If you check intake and exhaust lobe lift and multiply it x1.5 and it's up in the mid to low .500s, you can assume that you've got a cam that was made to run in the higher RPM range.

If it doesn't hit 500 after multiplying the measurement x1.5, you've got the wrong intake for your application.