This is where I get long winded...
I went with a 1972 Bronco Dana 20. I already had swapped a Dana 44 under the front of my YJ, and I didn't want to go through that again. There is no need to flip the Dana 20. It is driver's side drop. You can use the 32 spline output from Wild Horses and plug in your factory vehicle speed sensor with a speedo gear change. The Dana 20 is cheap (found them for around $600 rebuilt), easy to find, easy to twin stick, and easy to rebuild. I have right at $500 in mine including the cost of the case. The other thing is that the 300's are a very popular case. That means more $$$. The Dana 20 has the same weakness that the 300 has in its output shaft. If you were running a healthy V-8, I would say 300, but... I rebuilt mine in the garage. If you are even semi-mechanically inclined, you can rebuild it.
Here are the cons of the Dana 20... The case after 1973 are something around a 2:1 low range. Not what you want. A 1972 and earlier have the better factory low range of 2.43:1 You have to find an early bronco Dana 20. The jeep ones are passenger side drop and have the goofy "Texas" shaped bolt pattern on the front of them that bolts it to the adapter between the tranny and the t-case. An after market gear set that can only drop your low range to 3.15:1 is available, but not cheap. If you are into crawling, you will need a better low range than the 4:1 first gear that the 3550 offers. This is why I chose the NP-435. It has a 6.69:1 first gear. It is only a four speed. That is viewed as a detriment by some and a bonus by others.
Now, this is where it gets expensive for you if you crawl... Another option that is very small, and effective would be to put a Klune V in between your 3550 and use it as your adapter between the tranny and the t-case. It would give you the first gear of 4:1, another reduction of 4:1 at the Klune, and the stock low range of the Dana 20. This arrangement is shorter than the stock NP 231 WITH an SYE.
A separate bonus for you on this swap is that the Bronco guys are doing it. The 3550/Dana 20 adapters are readily available.
You will have to determine what style of wheeling suites you. If you haven't, go wheel the snot out of it and find what works for you. Hang out and wheel with other jeepers. Find out what the local folks are doing in your area that works for the local terrain. I would read as much as you can on line from technical sites. This is not a bad knowledge based site because we all have the same 4 banger and understand. A lot of BS bulletin boards will tell you to ditch the 4 banger and give you the big fish stories. I would start with this site:
http://novak-adapt.com/Check their technical library. These guys have their stuff together.
