Engineering is going to cost less than $300. Those universal rails still need a fair amount of modification (welding) to get them to fit. And depending on what seat you are putting in you may need to get a seperate seat belt anchor attached to the floor instead of the seat (like the stock ones do).

I reackon get a bracket from ebay usa that will bolt in and take it to an engineer. Ask them if it would pass engineering. If not get it strengthened. I think it would still be a better starting point than the universal ones.