Welcome aboard Larry! Since this is a restomod I'll move this to the Modified forum for you.

Larry, I'm sorry no one has responded yet. If you are a club member you can look at the top of the page and hover over the button that says Rosters. Click on Technical Advisors from the drop down menu and look for the Technical Advisor in the area of concern you have. Access to Technical Advisors is one of the benefits of club membership.

Larry,

I may be able to help you. I looked up in my 1929-1954 Master Parts Catalog and found the General Motors part number for your rear springs (part number 605383 in section7.503). It appears that the rear springs fit 1940-47 four door sedan, coupe, pick-up. 1948 four door sedan, aerosedan, 1948 sedan delivery, 1940-48 Town Sedan, coupe, convertible, 1949 -53 all passenger heavy duty except Sedan Delivery and Station Wagon. The springs have 8 leaves. I entered the part number in google and found the springs as well as the shackles and special bolts with grease fittings are available from The Filling Station.

If you think copies of the parts book pages would be help full let me know. I had springs made for my 50 Sedan Deluxe at a local spring shop. The cost was a fraction of the asking price in the catalogs. I may have a pair of 54 springs floating around. I do not know if they would be applicable to your project.

@larry-waibel Larry, If I Remember right, the original rear shackles for your car have a right-angle bend on one of the side straps. If your shackles have this feature, I can help with new old stock shackle kits. 

It is my opinion that the original rear springs would not be suitable for use with a modern drive train. The original enclosed driveshaft (torque tube) prevented any twisting effect on the springs during starts and stops. Original springs might not be able to withstand this stress. Replacement springs might still be using the original style shackles. Let me know if I can help.

Mike

I was going to echo what Mike said above.  The rear suspension set up should have been modified if you are no longer using a torque tube.  In the original configuration the torque tube kept the axile aligned.  If that was replaced with a drive shaft something would need to be added to prevent the axile from twisting under load.  also the torque tube by design kept the pinion angel correct.  This would not be the case if a drive shaft was used with the original set up.