I would like to install ,myself, a FF forend on my LR-308 but I don't have the .308 upper receiver block and I dont want to pay the 70 bucks that Brownell's has them listed for. Is there a way to do this without it. Especially one that does not involve me warping the upper receiver?

I've done 3 or 4 ar10 uppers without a block.  What I did (alot of guys wouldn't approve) was to use a hardwood board across the top rail the full length and another on the bottom, making sure the bottom one fits between the lugs with no gap.  Lay this in a vise sideways.  Make sure the jaws are centered on the center line of the receiver (up and down) and don't apply too much pressure, but enough where the receiver will not twist when torqueing the barrel nut.  I suggest at least a 5" vise.  Be careful because if something does go wrong, the guys here will never let you (or me for suggesting) live it down.

It's worth having the vise and vise block, and barrel wrench.  

I've done a lot of AR15's using the wooden blocks, and bench vice, with flattop uppers.

I don't know that I'd risk it with an AR-10 upper, though, considering how much more pricy that upper is, than your run-of-the mill AR15...

Knowing me, I'd probably go for it, but I'd also recommend people not doing about 50% of the things that I've done. ;)

Buy the proper tools for the job.