I have finally got the 4.6 running in the RRC, actually it has not been that hard so far.. but I have some irritations.
On startup cold it takes a few seconds for the oil light to go out. This I find a little odd as it then takes 12 seconds after shutdown for it to come back on. If restarted quickly afterwards it goes out immediately. if left for a few minutes it then stays on for a few seconds again . Should this be expected or have I an issue? the oil pump is from the original 184K 3.9 (The 4.6 has the 3.9 cam and distributor, the cam is new with new tappets)

Apart from that I appear to have an oil leak from the right hand rocker cover, or I spilt more oil than I thought filling it and possibly from the right had of the front cover where it meets the sump, again this could be dripping down form overfilling it.

Any advice on setting the timing? as there's a lot in the way of the timing marks!

Can't help on the oil pressure issue other than, what grade of oil are you running? Albeit the distributor driven type, I refaced the oil pump cover and put new gears in it and had no issues. Why didn't you renew your oil pump whilst it was in bits? I suppose if it was fine before you might assume it would be fine now. Although why is it taking time to build pressure??? Have you tested the switch or do you have a pressure gauge to see what the actual oil pressure is?

As for timing, set it to... something so it runs and not knocking/pinging/pinking. Take it for a spin and using a 3rd or 4th on a bit of a hill, floor it, stop and advance timing a smidge, rinse and repeat this procedure until it knocks/pings then retard the timing until it doesn't. I did this as the timing marks on mine were... out and not very accurate. Actual TDC for piston number 1 was not the TDC marks on the crank.