From what I've been able to find out, the Cat 3406C, Cummins N14, or Detroit Diesel Series60 would be appropriate. The Detroit V8's & Caterpillar 3408 are too "old" for the Ford LTL9000. Stick with the 3406. I'm not familiar with the transmission that's in the kit, but the "standard" transmission was a 9-speed direct.