I'll be firing up a fresh new, never run before, 383 stroker engine soon. I'm wondering What type of oil and viscosity to use? Amsoil with zinc was recommended so far but not a viscosity. Also, the start up/break-in procedure? Pre-spin the oil pump first? Run to what RPMs? For how long? Etc. Run it for how long before changing out initial oil? Replace with what? All the details. I'm a newbie in case you couldn't tell.. If there is already a pre-made document with all this info maybe you could provide a link?
Also, I have a pre-run (broken in with some miles on it) TH200R4 tranny. Is it ok to use Mercron type fluid in it being a Chevy and all?
Thanks for any and all help.

 

Addressing initial startup of your engine first.
Reputable engine builders provide all the information you're asking about. Your questions lead me to deduce that the engine builder is unknown. If that's the case, I would start by double checking EVERYTHING. Check the torque on the piston rod caps, crankshaft caps, cylinder heads, etc. Double check the initial adjustment of your lifters.
If you haven't already done so, prime the oil pump by smearing a thin coat of petroleum jelly on the gears. This prevents galling while providing good suction for the pump to draw oil up from the oil pan.
Use 20-50 weight oil with high zinc such as Valvoline VR1 racing oil.
Attach an oil pressure gauge to the oil port near the distributor goes.
Prime the lubrication system by spinning the oil pump.
Check the oil pressure.
This next step is critical and you may need a helper; with the valve covers off and the oil pump working, rotate the crankshaft by hand and observe the rocker arms to confirm that each one gets oil coming up through the pushrod.
For RPM and duration, follow the camshaft manufacturer's instructions. If you cannot determine the manufacturer of the cam: run at 2,000-2,500 for 20-30 minutes.
During cam break-in check for leaks.
After cam brake-in, change oil (and filter) to whatever you intend to use on a regular basis.
If you have solid lifters, make your final adjustments now while the engine's still at operating temperature. If you have hydraulic lifters, you shouldn't need to make any adjustments unless you heard excessive valvetrain noise. Dealing with that is a separate issue.
When driving, from a standstill, gradually open the throttle all the way until 3000 RPM; this helps the piston rings to seat properly.
After 1000 miles, change the oil and filter.

Good luck.