Since you enjoy drag racing I would also look at installing a roll bar system. Yes the sub frame connectors do add some strength but not much. They use the cheapest steel for sure. If you did make your own I would look at getting some HSLA, High Strength Low Allow which is very forgiving to MIG or TIG welding and does not require annealing of the welds. Will be more than double the strength of CR Box tubing.
You might also see if a supplier has any of the UHSS, Ultra High Strength Steel which will be 4 time the yield as CR. I was an automotive product, process and tooling engineer for years. These new steels are how they are improving the handling, crash abilities and weights on the new cars. For is even using in outside skin panels. If they get bent in crash no way to hammer out and fix you have to replace the panels.
I used the UHSS in a redesign of the John Deere Combines to take weight out but still make the unit stronger.
I am hoping to get back on my 72 Q vert and I need a roll bar system to be able to run track days without a speed limit. I am also looking at putting extra metal inside the rocker boxes so not seen and are at the widest point to gain the most. Will also have at least a 6 point roll bar. Bar tubing is DOM Drawn Over Mandrel so no weld seam like regular box tubing. All tubing starts out round and is rolled into square or rectangle.
The biggest gain in rigidity will be from a roll cage with the long triangles that are generated. The height of the sub frame connectors is just a couple inches so the bracing will be minimal compared to say over 3 feet on angle on a roll bar. Any space frame design will always be stronger and lighter. There are suppliers that make the bar kits but I have not checked I have a bender for 3" dia. down to 1/2" so I can make what I need.
BTW if you use 4140 Chrome Molly steel you should check into the process to anneal the welds to prevent stress cracks later at the welds. It is strong but not as good as the new steels are. When ending a weld you should tail it off away from the end of the joint. That helps prevent a stress point. Any plates should be put on with a curved end to weld so that you do not generate a line that bends easier. Take a look at say the lifting arms on a 2 post lift. A good design will have curved ends on all the brackets welded on. A sorry design will have straight across welds that produce a high stress area. Might also look at a track hoe or dozer to see how they do the welds. Not rocket science but there is some science to it.
Had MRI done Friday know tomorrow if my back is totally gone or not. Maybe they can put a connector in me to keep me going, lol.
Don't be afraid to go on your own for sure. There is no design that cannot be made better.
D
Thanks for the tips 10 point cage will be going in and I hope to tie everything in together. I do alot of structure welding at work I'm sure its same fundamentals. I haven't decided on chrome moly yet or not. It sounds nice for weight savings. But to be tiged correctly