The 300 shares a mounting pattern with the SBF so anything that fits a 302 will fit a 300. The balance is different, so you need to retain the 300 flywheel. There are 2 five-speed truck trannies that were used behind the late model 300. The ZF used in the F250/350 is an extremely durable beast but it is heavy and has very wide ratio gears (5.72/2.94/1.61/1.00/0.76). The Mazda built M5OD is lighter, weaker but still has ratio which are inappropriate for a car (3.90/2.25/1.50/1.00/0.80). The V-8 version of the T-5 (3.35/1.99/1.34/1.00/0.68) is a better bet but even in the World Class versions it is only rated for about 325 ft-lbs, which a moderate 300 can easily exceed. Next step up is the aftermarket CR version of the same box which has a 2.95 1st and a .63 5th but is only marginally stronger. After that you're into $$$ with either the Tremec aftermarket boxes or the G-Force reworked T-5 which is a thing of beauty but at a significant price
