Nissan Hardbody engine overhaul

[HardI3odyD21]

Newly registered to the site long time browser, I have a few questions that I would greatly appreciate if any one can answer without to much guessing more solid experience and knowledge cause I'm far from a mechanic myself...

I have a 1993 Hardbody 2.4 auto with 165000 + , recently wanted to do complete overhaul due to mileage and oil mixing with water but was stopped by my cousin who is doing all the labor he told me only need to rebuild head completely and a few other parts (i.e. Water pump oil pump timing chain kit radiator and all hoses few other small parts) after tearing it all down and building it back up he told me he is having issues with the timing it will crank but no rev what could be the problem with that?

2.I was told by my cousin to use 20w50 oil cause there is a light sound coming from the block and we live in Palm Bay Florida were the weather is a constant 85* and above, I just want to know if 20w50 is a safe oil to use since I was told not to use 10w40?

3. What are all the parts that I could have replaced in the block if I would have went ahead and overhauled everything?
Any recommendations and further info will be greatly appreciated...

[ezb57e]

Could be many things keeping it from starting. Hopefully the timing chain is on right, and the distributor is in right. Beyond that, connectors, grounds, who knows.
I would use 5W-30, or 10W-30 if you are in a really hot environment.
The heavier oils don't get into the tight clearance areas of an engine like the valve lifter, cam bearings, quick enough after all the oil has run down over night, and this can cause some unnecessary wear.
If you are trying to rely on a heavy oil to fix a noise, something else is wrong.
Id sure use 10W-40 before 20W-50.
The rings and rod and main bearings are typically replaced at a short block overhaul, also rear main oil seal. Piston and pin condition would also be inspected.
The cylinder walls should also be checked for taper and out-of-round, and possible re-bored and new pistons fitted if needed.
Did the old head gasket show a failure that would account for coolant in the oil?