I found a good condition J37 head from a 3.7 TL, and I'm thinking swapping my J35 head (4g 3.5 TL). Is it a direct bolt on? Do I need any modifications?

I have compared the head gasket between j35 and j37. The coolant ports match, but the tiny ports (for oil I guess?) aren't.

 

Good question. If the head gaskets are different that probably answers the question right there. Also, I'm not certain what the performance differences would be. Lastly, vtech is present on both intake and exhaust valves with the 3.7L engine but only intake with the 3.5L. Since that's electronically controlled you're then getting into ECU territory which is likely going to cause issues when you swap heads.

 

Dah! Vtec not Vtech! Can't believe I made that mistake