Has anybody moved their springs inboard on a d100? How'd you do it? I'd like to get the extra little bit of room for my budget racer since I gotta weld new spring perches anyway to swap the axle on top. I'm thinking I might be able to fit my 15 x 15 supertricks under there with the springs on the inside of the frame rails

I have moved them them directly unnder the frame and then put the axle on top of the spring. This gave me enough room far a 14 X 32 drag slick without effecting the ride height.
I used front spring hangers and rear shackel mounts from a B body lined them up to the outside of the frame rail and welded them in place.

rear

On my '84 I simply ground off the rivets holding the spring mounts to the frame. I welded a plate for mounting on the inside of the frame then swapped the springs side to side. I'm no chassis engineer but it was a pretty easy project. I'm using 31x18.50x15 rear tires with plenty of room after installing tubs. I used a narrowed rear from a car to move the springs under the axle.

I welded plates on the inside of the frame also on the 84 that I tubbed. I swapped springs and hangers to different sides, welded and bolted everything together. I ran 33x21.50's with very little room anywhere. It worked, I used poly bushing in the springs because of the lack of clearance.

Thanks for the replies. That's kind of what is was thinking I would need to do. Anybody have pictures of the hangers on the inside?
Ps mine is a stepside box so I should have plenty of room for anything I want it looks like as long as I have correct back spacing

On my truck to make room for the springs on the inside of the frame I had to eliminate the original gas tank and mount a fuel cell under the bed behind the axle between the springs. A 16 gallon aluminum cell fit well.

I used a shackle flip and axle on top of springs with A-body 8 3/4 to fit 12" with 4.5 BS rims with a 29x15x15 M/T in the fenders with bed tubbed.

I would suggest an A-body 8 3/4 with springs in line with frame rails. perches should be around the 41" center as a truck/a-body share the stock 43" perch center already.

this should allow you to go from a 12" rim to a 14" rim adding 2" to the backset of the rim then tubbing flush with the frame.

here it is before the bed