It is a fun mod, Be prepared to do some major modifications. I run one in mine and love it, BUT, I built my Bronco around the 300/NP435 combo. Major Mods will include.
Motor crossmember
Trans crossmember
core support
Possible firewall mods
Clutch linkage
The motor has to be moved toward the rear no less than 3 inches, and that barely gives clearance of 1/2 inch from the fan and the radiator with the radiator moved a little forward. you could mod the core support to move the radiator forward to the max.
When the motor is moved to the rear the intake interferes with the firewall unless you center the motor, otherwise you will have to mod the firewall.
The trans crossmember will need to be moved back also to accommodate moving the motor backward.
If you do the swap you will fully enjoy the end product, Being able to wheel all day at idle while the v-8's are all wound up.
You can check my build thread for more info.
http://classicbroncos.com/forums/showthread.php?t=155542
(Get some popcorn, boiled peanuts, a beer or 12 and enjoy the read)