Oil/O2 Questions

[foss40z]

Hey Guys. I would like to get some input about a few things if i could. I recently did an engine swap from a 88 2.9 to a 91 2.9 and would like to know what oil to run and weight. I am leaning towards full synthetic but do i go with a 5-20 or 5-30 weight. the engine has 70,000 miles on it.

Also i put on a pair of pacesetter headers on it with no hole for the o2 sensor. i read stuff on it will make the engine run rich and will lose a little miles per gallon. how many miles will i lose, and will this harm the engine in anyway?

I know some of you might be thinking why did this tard put a 2.9 back in his truck lol. my excuse is i got the engine pretty cheap and i dont have the time to do a 4.0 swap at the moment for im moving in month.

Thanks Guys
Mr.Foss

 

[foss40z]

after research i will run 5-30 synthetic being im in a warm location year round .

about the sensor can any1 help me on this with any information they might have? will it damage the engine in anyway?

Mr.Foss