7 1 0 F r o n t C r o s s m e m b e r
One of the trickiest conversions I did to my 510 was to swap out the front crossmember for one from a 1976 710 wagon.
The early year 710 cars came with some factory goodies that were intended to remedy some of the suspension evils inherent in the cars when they reached the shores of the US. I caught wind of the fact that Datsun employed longer front control arms in the 710s and also used 5mm offset strut mount insulators.
710 Offset Insulator PN 54320-U7000
I never had any luck finding the ever
so elusive 5mm longer control arms, but they do exist since the Nissan part numbers are ____________ . However, what I did find by crawling underneath several 710 wagons, was that the 710 crossmember is practically identical to the 510s. The
"so what" is that the control arm pivot points are not only higher than the pivot points on a 1969 510 crossmember, but they sit further out towards the outside of the car also. This means for more correction of a lowered front end on the 510 if installed. Unfortunately, the installation is not without it's work.
Now I said it was practically identical because one main difference is where the 510 has fixed engine mount pedestals, the 710s are completely removable.
Additionally, you have to remember that the 710 came with an L20B. First of all, the crossmember will bolt right into the 510 and the control arms will bolt into place without any axial alignment problems. However, the engine mounts will set the engine so far back that it will leave about 1/8" clearance between it and the firewall. This means everything else will be pushed back - transmission, driveline too long, etc. What I did was I had to figure out where the stock engine sat with regards to the axis.
Measurements from stock cars gave me an idea that the mounts needed to be moved about 29mm forward. 
I
was able to tap the crossmember and bolt the mount bases forward on the crossmember. Then I tried dropping the engine in using the L20B engine brackets (the ones above the rubber mounts). The engine sat much higher than a normal L20B drop using 510 stuff. So I then used the L16 engine brackets with 710 from the mounts down and this was nearly the solution. In order to make it fit right, I had to grind the bolt holes oblong, giving me the 6mm adjustment I needed on the 710 mount base, in order to allow them to sit at the right geometry under the weight of the engine. With all this done, the L20B now sits slightly lower in the car than the stock L16 did. Clearance between the oil pan and the
crossmember is about 3/8" at the tightest. After my first trip to the alignment shop my camber readings up front were -1.17 left, -1.58 right. My coilovers may not have been exactly the same and I'm sure that contributed to some of the deviation between sides.
1 5/8" pivot height
Detail of mount in new location
Top View of Crossmember
Detail showing 4 pieces (from left to right: Engine Bracket, Rubber Insulator, Insulator Cup, Mounting Bracket