X10. The heater core is a tiny POS with tiny passages. I had to replace a leaker it was no fun........
Hard to see here, but the original was VERY thin, only about 5/8--3/4" thick on the core. NAPA listed two, and I ended up sticking the larger one available in there. You can easily trim some projections out of the enclosure, and the "heavy duty" one fits right in. This was a previous Dakota I had for a short while, a 2x4 V6. If I'd kept it I might have saved myself some trouble LOL