When I swapped in my solid axle, I did not need any driveshaft spacer. I used the correct pinion flange to adapt the stock Cobra driveshaft to the solid rear. If you need the part number, I can dig it up for you.
Yea, I transferred the pinion flange from the IRS to the solid so I could still use my stock driveshaft. The problem is the slip yoke is not totally engaged with the tailshaft of the transmission like it should be because the solid axle has moved the pinion and everything back about 0.75" or so. I am just worried about a failure at the slip yoke since it has significantly less engagement.
That's weird. Do you have adjustable upper/lower control arms? If so, maybe you could adjust them to bring the rear end forward some. I'm searching around the web right now for driveshaft spacers....no luck so far. Worst case scenario would be having a machine shop custom make something. If I find any spacers I'll report back.
EDIT: I found this info. Might be the only option. I checked the Steeda site, the spacers run $49.95. I just read that HP By Hermann sells driveshaft spacers too, so give him a call.