Hot Rods Model A Frame Welding Questions

I am about 10% through building a 30 Ford sedan as a 50's hot rod. As I am getting ready for the frame questions arise.
1. Use the frame as is.
2. Sandblast and weld in the original cross members before use.
3. Drill out factory rivets, sandblast and weld back together.
4. Frame boxing plates - yes or no - engine is Merc Flathead ,
guestimate 150 - 200 HP

Any comments helpful.

Thanks