The 2.3 diesel and the 2.6 gasser are completely different engines and they do not share any parts. If you are running a head with cracks on a diesel your just asking for problems. The 4D55 diesel runs at a 21:1 compression ratio so the parts need to be built much stronger. Like I said you need to get a new head from Heads R Us. The 4d56 heads are redesigned to prevent cracking. Also the KM145 is a descent tranny, I think your expectations of a 20-30 year old transmission are too high. If you went out and had a km145 professionally rebuilt it would last for another 20-30 years. To me that seems like it's a decent tranny.