I see all these efforts for crossmember modifications. I read that the poster wants to make a temporary one to support the frame from "shifting". Not having a good look at the AD frame in person or what different motor/trans combos are contemplated, I am giving a general engineering opinion mixed with my crossmember experience.
It seems the issues folks are solving are:
1. Removal of original motor crossmember to allow a new motor/trans clearance. The removed member is near the rear hanger of the front leaf spring. Which, when removed, some believe would causes the frame to deform during operation and cause something to happen.
2. Adding/designing/fabing a (dropped for clearance) replacement for this crossmember to clear a new V8 and auto trans on their way back to a new support member.
3. Adding/designing/fabing a crossmember and support for a new transmision which is located at X distance rearward of the original.
4. Adding/designing/fabing a new motor mount for the V8 Mouse or Rat.
So the challenge is presented. Many ideas. Many designs. Many theories. Here's another batch of those from little ol' timid me.
1. The tubular crossmembers that are available are cheap, already fabricated to the approximate desired shape. Dropped. Universal. Few pieces. Boltable. Strong. Elegant. Adjustable. Not much fab work. No welding unless desired. They are crossmembers! Tubes are used all over hot rod suspension, roll bars, supports. Provides a strong one piece custom shape.
2. Some folks abandon the original crossmember and do not replace it. A "C" shaped channel frame is pretty strong. The side loads from a leaf spring hanger are not huge. If the new crossmember is strong and not too far away from the old crossmember, my engineering gut tells me everything will be fine. Some of the designs I have seen are not doing much. My first reaction was the same as Hot Rod Jerry's. No gussets. True, they have been used for years and no issues. That could be because they are just extra weight metal and have no function. I won't judge because I don't know for sure. The one's that are not carrying a motor or trans load, are not hurting anything.
3. If you want to replace the original because you feel it is necessary. That's fine. Derivet the entire old member and install a universal tubular crossmember. Either one for a transmission or one for a motor. Whatever has the best shape. Bolt it on. If the adjustable flange ends of those tubular crossmembers can be welded to the tube and the whole thing can still be removed, that's the best method. Maybe it would never have to be removed depending on the other clearances. I know it can be extreme pain to derivet the old crossmember. But schlepping onto the cut off part is not the right thing to do. Takes a lot of time and effort. Can't stick it up there, mark and mount it like you can a Universal Tubular. You have to measure, design, cardboard it, and keep testing, cut some pieces, tack it, clamp it up there, then final drilling and welding.
4. Use two more of those universal tubular crossmembers for the motor and trans.
5. Some builders are also changing to IFS. The leaf spring side load support issue goes away. If there is a IFS frame boxing requirement that interferes with a universal motor crossmember, work it out/mock it up.... or use a different motor-mount-to-frame part/design.
Contrary to popular belief, I am not a Cross Member.
