Thanks, Stuart!
I will probably change my plans a bit. My rig has dual antennae mounts on the rear. Two 524s in doghouses is going to take up the entire cargo area. One functioning radio is cool, but do I really need two? I have a lead on two doghouses, but shipping from Canada is going to be expensive, considering the MT-1029A mounts are about 19lbs by themselves. So...
I will probably remove the second antenna mount tower on the rear.
Unbolt one of the rear seats. Install the doghouse closer to the front seats, then bolt the passenger seat to the top of the doghouse, facing the rear.
This will save room for an old Pattern 82 Rucksack on a US ALICE Frame, or CadPat Ruck, if I can find one.
Buy the reproduction front brush guard antenna base to install the PLGR GPS antenna, and an old style plastic PLGR mount between the front seats.
I found some pics of the Rifle Mounts between the front seats and the rocker panels:

It doesn't appear to be the old M151/M38 Rifle Mount.
The closest I could find are these surplus Bundeswehr vehicle rifle brackets:
I'm scrounging parts to build a C7A1 Rifle and a C8SFW Carbine for displays. Both will be US-legal semi-autos. Not spending the cash and not have them shoot.
There is a US Mk85 Pintle Mount that I can fabricate a mount block that fits the top rollbar:
I'm wanting a C6 GPMG as a display piece, cover all the basic infantry weapons in use by CF. There are three different airsoft FN MAG guns, one made from steel, two in aluminium. The steel version is almost actual weight, but is $1550:
Inokatsu mfgs FN MAG58 in both Alu and Steel:
http://poweredgeusa.com/Inokatsu/Oth...Inokatsu-MAG58
I just need to find a couple M72A5 LAW Tubes to bungy cord to the rear rollbar tubing.