Please help me diagnose this 273

No 1. Take the cap off and see how far you can turn the crank back and forth before the rotor moves. That is how much play that factory nylon sprocket type chain has That will efect compression.

No 2. Adjust the valves they should be solids in a 67 273. start there.

You may need a distributor also you'll find that after you get the compression correct.

One thing I thought I would bring up due to the intake installed.

I always see guys check the compression with the carb closed at idle position. Check it at wide open throttle also. Compression can vary from cylinder to cylinder at idle position if you have a bad intake leak on those ports. Check it both ways. You did say the guy installed an intake.

This may not be your problem but here is some info for every one.

Port alignment will effect the car a lot if you have a 340 intake on 273 heads or the opposite Like a LD4B wher you should have been using a LD340 due to the fact that the ports are narrower and wider and can be misaligned easier.

The pins front and rear in the center of the block can change port alignment also if he used a intake that was drilled for a different motor .

When installing a new intake put a mark at the top of the center of each web on the intake where you can see the center of each web between the ports while installed. Those lines you put on should align with the exact center of the valve cover threaded holes.

If they don't move the intake around to get them as close to equal as possible. When they are where you have the intake positioned where it aligns the best to all ports , Tap the intake using a leather mallet. This will put marks where to drill the pin size holes in the intake to keep the intake in the desired position using the pins in the block while torquing. Even if you use Gasket maker instead of a gasket you should still use the pins. Put an intake on loose without pins and see how much you can move it front to back . It do't take much to have misaligned ports

I use those pins on every small block. I have seen many removed when they buy a new intake because the intaked are not drilled. Why do you think new intakes come without being drilled but the protruding bosses in front and rear are always there for pin support.

The valve cover bolts are always in the center of the web.

even if you use factory iron heads and a Iron intake off of a different engine this can be off. Its worth checking. Its easy and no special tools required when installing your intake.
A balanced charge of air/fuel is just as important as mechanical balancing. This was the easiest way to explain this .

This is what I have done for years. Some may not agree There are always the critics on this site .