Oil is primarily heated by rpm's. High, sustained rpm's, like you see in road racing. Unless you're racing, you have no need for an
oil cooler.
My first suggestion would be to disconnect the cooler, and just leave it in place for looks only.
There are a number of thermostats available. I like the type that bolts in place of the
oil filter adapter; commonly called a sandwich type. Plenty of room to leave the filter in the stock location. Earls makes a good one that I've used before.
Earls also makes a good in line type. But it takes more fittings, more room, etc.
https://www.jegs.com/p/Earls/Earls-T...72463/10002/-1