Timing Question
 

I know that I'm supposed to set timing to 5° ATDC at 900 RPM and then check it to see that it's 35° BTDC at 3500 RPM.

Here's the question: Is the second check at 3500 RPM just to make sure the distributor advance is working, or should you actually time it at 3500? Also, if you can't achieve 5° ATDC at 900 RPM and 35° BTDC at 3500 RPM, does that mean the advance isn't working properly and if so, then what?

The second check is done at 6000 rpm. What the timing is at 6000 rpm is more important. It should be 35 deg BTDC at 6000 rpm. Does your car have a vacuum connection on the distributor? Do you have MFI or CIS?

My care was converted to Webers by the previous owner and it doesn't have a vacuum connection. I thought the 5° ATDC at 900 RPM was with the vacuum removed, no?

I would not be concerned with the 5 deg after at 900. No vacuum advance is not a problem, since that was for smog, it is my understanding.

Just make sure that the total advance, when you rev the motor toward red line or 6000 rpm, is 35 degrees . In fact your motor will idle better if it is 7 -10 degrees BTDC at idle.

My care was converted to Webers by the previous owner and it doesn't have a vacuum connection. I thought the 5° ATDC at 900 RPM was with the vacuum removed, no?

No. The 5 ATDC spec is for engines with vacuum retard, not vacuum advance, and it is measured with the vacuum connected. Vacuum retard was an emissions device for the HC curb idle test and does more harm than good. Vacuum advance is for fuel economy, it is a good thing, but your engine never had it. The factory spec is 38 BTDC @ 6000 rpm