There's a 2011 mdx motor for sale that snapped a timing belt for 300 close to me. would it be a good idea or even worthwhile to buy it for the heads, put new valves on it and bolt it up to my 3.2? I plan to rebuild the engine in the future with the 3.7 crank and heads but right now I don't have a shop or garage.

 

you would also need the accompanying manifold runners.

if you're not tuned, or are not planning to tune after the head swap, you'll likely see a loss of power...
after you get the 3.7l heads on you'll need to tune to see an increase of power

 

It comes with the runners as well, would there be a noticeable increase in power after tuning?

 

You might well get a few ponies up near redline, however, given the larger intake valve diameter (1.378" vs. 1.417"), you will lose mid-range torque in the process. Yes, flat out, the engine will be slightly more powerful, but around town it will feel more sluggish.

 

Get the whole block!!! use the crank and heads plus upper end parts for better power. 2011's have issues with piston rings and cylinder walls so you will not be able to use them unless it's not damaged from the issue. Rebuilding the J37 heads you can go with better than OEM parts and get a nice engine built. I believe J35 from ody and J37 crank make a franken 3.6L.