I have a 70 long bed. How low can you go without cutting the bed? I’m putting Crown Victoria suspension under it and just wondering how low I can go and any pointers on leveling the rear with the front. I’ll be putting cv rear in too.

 

So measure down from the bottom of the bed floor (where the rear end would hit it first)to the top of the rear end pumpkin. Most street suspensions have +/- 3” of suspension travel which is dictated by the travel in your shocks. Then you need to take in account for a bump stop (1” is typical). Now take your measurement minus the suspension travel minus the bump stop and that is as far as you can lower the truck relative to its current height without cutting the bed. This is all very general but it will give you an idea.

Even to get it this low you will most likely need to C notch the frame.

 

If you are using rear suspension (correction from IRS thanks Aerocoupe) from the CV then you won't be notching the truck frame. You'll be grafting in the CV setup. You'll definitely be cutting the bed floor if that's what you mean. This Youtube series shows you what was done to swap in the CV rear suspension. Several maybe 20 episodes.

There are more YouTube series that include the CV rear suspension swap.

 

Pretty sure the OP was asking about the rear being the question was "How low can you go without cutting the bed?". The CV IFS (not IRS as they did not come with an IRS) will lower the front right about 5" from stock if you use the stock CV suspension parts. Not being a smart *** here just wanting folks to know the correct terminology. Lots of folks have dropped the rear of the truck keeping the stock leaf spring rear suspension by the following:

2" Drop
something similar to the DJM rear leaf spring 2" drop shackles

3" Drop
flipping the rear end to the top of the spring which requires cutting and rewedding the spring perches and setting the pinion angle. Axle tube is 3" hence the 3" drop.

4" Drop
install something like the DJM hanger and shackle kit

From these three options you can also get a 5" or 7" of drop with stock spring pack. Some have messed with the spring pack to "tune" the rear drop. This will affect the spring rate so be mindful of that. You can also order new rear leaf springs, bushings, and rear shackles with the correct drop. Another option is to four link the rear and use coil overs. This allows you to set the ride height upon installing the four link and then tune it with the coil overs.

My apologies if you already knew all of this but thought it was good info but again how far you can lower it without cutting the bed is determined as I stated above.