I have just put e new crate engine in my Vette and the engine seems to run fine, a little rough but thats probably because i havn't got the timing perfect yet, but what concerns me is NO OIL pressure, I suspect the sender unit, does anyone know how i can test this before i start a major search else where

Install a mechanical gauge in the pressure port, where the electrical sender is now. Then, disable the ignition, and crank the engine over for 5 seconds or so. You should see oil pressure on the gauge. If you do NOT see any pressure, STOP!!! You must find the problem before letting it run any more!!!
If you do get pressure like this, then you have one of several issues...
One is the sender itself,
One is the gauge itself,
and one is the wiring between the two.
A quick test to check the wiring AND the gauge is to ground the wire that goes to the sender. With the key on, your oil pressure gauge should peg out on the high side. If it does, the gauge, and the wiring is good. If it does not, then you'll need to dig deeper.

I suspect your sender is bad...or not connected.

OK, here's the temporary update more will follow later, I grounded the sender wire and the gauge shot to the left !, OK not what I was expecting, however maybe that is correct, not wishing to dwell on that I figured I had better take the cam covers off, hhmm not very OILY, OK out with the distributor and in with my home made priming tool attach it to drill and whirl away, I could feel some resistance as if the pump was pushing oil but NOTHING came out of the pushrod holes, therefore I have a problem, this is a new crate engine and monday I shall call the GM dealer where I got it and see what he will do, one thing I did notice and that was the shaft on top of the pump that the distributor connects to moved around a hell of a lot, i.e. side to side, it would no come out but didn't seem correct.

We installed a GM crate in DNV's '80 yesterday and we primed the pump with a priming tool and drill.  It takes quite a while(minutes) to to get the oil up  - also do not turn it too fast - just medium speed with the drill - it seemed to take a long time to get it up there but once there, it was OK - try again if you were expecting it quickly

The priming tool has to block off the camshaft galley to get oil pressure, make sure it does. You can't just turn the pump shaft.

OK just to make sure I am not giving myself more grief let me give you more details of the saga.

Gary;

I'd try bourbon or scotch...

My pumpshaft did not move side to side.  The tool we had had a disc that was fitted onto the shaft that, while I didn't know it at the time, is the correct width and height to block off the camshaft galley. 

It took in excess of 3 minutes to get oil starting up with the drill on low speed, but when it started to flow, it first came into the heads and then out the pushtubes.

I would seriously think about pulling the pan and seeing if everything that is supposed to be there is there on the pump.  It is held in place with bolts and when dropped should have 2 gears in it. 

The spring tension determines the pressure from the pump and the screen should hopefully be tacked into place with a tig or braze, not just pushed up in place.  If there are parts in the pan, that would be bad.

Remember, new does not mean right or perfect.  GM Crates are not built here anymore (not that that means anything) but new parts can fail just as easily as old ones.  71Shark can attest to that and so can I.

You are doing the right thing taking your time.  I can well attest to how frustrating it is.  Look under my name and find all the engine posts I have had, starting out with finding a 305 in the hole where a 350 goes

Follow these guys advise and you'll get there.  I really would consider dropping the pan and the pump to see what you can see.  Alternatively, contact the place you bought it from prior to this and ask them if the shaft should be loose and not pumping oil.

The Saga continues....................

OK, this should be the end off the saga, GM took the car in and after roughly an hour called me to tell me that I had the oil pressure switch in the wrong hole, there are two holes within an inch of each other and the one I should have used had a plug in it that I didn't see so I used the one I did see, and those of you that know this engine a probably wondering how I put the adapter in when its a different thread, well I was too clever for my own good, I re-threaded the adapter wrongly assuming that over the last 20-30 years they had changed the tread size (wrong again).

 

This of course did not explain the lack of oil at the top of the engine and I questioned them about this and told them I had spun the pump with an electric drill for quite some time, they informed me that it was not possible to get enough pressure this way and I would have to run the engine and assured me all would be OK, well i now have oil pressure and all seems to be OK, therefore my mistake cost me $50 for putting it in the wrong hole (about par for the course I guess) !!!