oil & 10% pulley

I bought a 90 SC in June; all I have done so far is the exhaust
2 1/2 into 3 into 2 1/2 no cats with a Dynoflow resonator, I will probably go with a 10% pulley. Will this be OK as far as head gaskets?

Also it's time for my first oil change, the previous owner ran synthetic 5w30 this seems a little week to me as I live in a warm Climate (Florida) any suggestions as to what weight would be best? I was thinking 20W40 synthetic. 80,000 miles

Any suggestions or input appreciated.

Hello. It sounds like your exhaust setup should be sufficient, especially if you have no intake upgrades. As far as the oil, If you have no problems losing oil currently I would continue the use of 5w30. This grade provides less friction upon startup, even in warm climates.. and most wear occurs at startup. Most suggest against the use of a 20weight 40 oil on a stock engine. These grades are usually reserved for those with significant engine upgrades. At most, 10w should be fine, but stick with 5 if you don't burn or lose any.