Lots of cam/valvetrain questions, need advice.

Once the cam is installed and the heads are on, use a roller lifter that has been made solid for tooling,(anybody you know have one? If not, you can make one easily), and get an adjustable pushrod(again, another tool), and mock it up on a cylinder. Set the length of the pushrod so that during the valve operation, the roller lifter(you'll have to have them for this, and yes, 1.6:1 is fine with your cam's lift),moves along as close to center on the valve stem tip as possible.
You don't want the roller on the rocker arm to be too close to the edge of either side of the valve stem tip for obvious reasons.
As far as springs, they should be matched to the cam. In this case, 550 lift springs should be good, as they will be less likely to float at higher RPMs. If you intend to race the engine regularly, perhaps somewhere about 580 lift springs would be better.
Just as a guess, I would say pushrods somewhere about 6.850" - 6.925", depending upon the length of the roller lifters used. Have your stock heads been outfitted with guide plates? You'll need them with roller rockers so the rollers don't roll off from the valve stem tips.

Oh yeah, follow the manufacturer's recommendations on cam install.
No moly on roller cams.

Here are a couple of articles:
http://www.compcams.com/Technical/Products/Pushrods/
http://www.trickflow.com/product/fordcylinderheads/rseries_sbford/pr_r_sbcford_pushrod.asp
http://www.grapeaperacing.com/GrapeApeRacing/tech/valvegeometry.cfm

Tool:
http://store.summitracing.com/product.asp?p=352&searchtype=ecat

I wouldn't go too wild on valve spring pressures unless you install screw in studs too. Springs made for a .550-.580 lift cam will pop the press in studs out of the heads.