Be careful just whacking 12 volts onto these glow plugs - you could kill 'em. It is best to run them through the relay as that not only cycles through the glow plugs but it cuts out if they get too hot.
As for using glow plugs - well a good engine will start without them so long as the ambient air temperature isn't too cold - it will just take a bit longer => a few more cranks - not hours and hours!
You can replicate the effect of glow plugs by blowing hot air into the intake manifold.
If you have a block heater you could use that too to get some warmth in there => but only use it if you've got coolant in there...
If I were you I'd change the engine oil - that will help it crank faster.
If you're cranking it on the stand - I'd be more inclined to do a compression test...
...and if there are problems move straight to a leak down test...
As for using glow plugs - well a good engine will start without them so long as the ambient air temperature isn't too cold - it will just take a bit longer => a few more cranks - not hours and hours!
You can replicate the effect of glow plugs by blowing hot air into the intake manifold.
If you have a block heater you could use that too to get some warmth in there => but only use it if you've got coolant in there...
If I were you I'd change the engine oil - that will help it crank faster.
If you're cranking it on the stand - I'd be more inclined to do a compression test...
...and if there are problems move straight to a leak down test...