420SEL runs w/o accessories?
 

Is there anything preventing the engine from starting if no belts are connected at all?

Thanks

No

Ok, then I might have a problem.

I changed the waterpump, which involved removing the harmonic balancer and distributor (and I also changed the belts), and now after putting things back together, the car will not start. The starter turns, but it seems like like there is no spark. I was careful to replace the distributor cap back at the marked point for cylinder 1, and put the balancer back on at top dead center (which is where I took it off from). Any ideas?? Thanks in advance. Any help is appreciated.

You might still have the the timing wrong. Remember that you want TDC on cylinder 1 at the power stroke (both valves closed). 360 prior to that you are at the end of the exhaust stroke. be sure yoy have the right TDC. Technically there are two during the 4 engine cycles.

Dpetryk - Thank you for the advice, you're were right on the money with that one. The car is in one piece again, and runs great.

Glad to be of help.