iceD wrote:Will those shorty 720 boxes go into a 510 with the stock drive shaft uncut?
They are both 26" so yes no shortening but the mount would still need some mods. Only a 2wd shorty would be worth trying. It has a speedometer drive in the tail. Four by four are driven from the trans case. You can see the tail is not machined, I wouldn't even try to do this.
They would fit, but your L engine would have to rotate to the left about 20 degrees, or the transmission 20 to the right, most likely somewhere between with the rubber engine and transmission mounts tearing apart. To do this successfully you need a front case from an L series.
If either of those 5 speeds were made after '84 they probably have the larger 62mm counter bearing on it. That won't fit the 56mm L series front case so just swap the bearings and front bearing cover. The 1st/2nd shift rod on the '85 is also 16mm and the L case is 14mm so just drill it out to fit.