I really like the way they tied the cage into the chassis. Looks good and should work well. I would add a horizontal tube as a gusset or plate gussets to make sure it wont bend or push away from the frame if it ever goes shinny side down...
What diameter and thickness tube are you using? Is it chromoly or DOM steel, I'm sure it is not EW with your emphasis on safety.
Great that you father in law will loan you the gear. I'd suggest a Hybrid neck restraint rather than the neck roll, that's what I use.
http://simpsonraceproducts.com/simpson/hybrid-sport/ It doesn't rely on the belts solely like a Hans device and the sport version is affordable. Impact has a couple HNRs similar to a Hans at the same price as the Hybrid Sport as well.
Also, you can find good deals in the clearance sections of Simpson and Impact racing. Another couple good sources for safety gear at good prices are PCI Race Radios
http://www.pciraceradios.com and UPR Racing Supply
http://www.upr.com. I hope that helps you to get your own gear without breaking the bank.