For those interested, here is a size comparison of the MSD8350 ready to run distributor (left) and the 8577. Both use the small cap, which is 3 7/8" in diameter. The stock Ford dual point cap is 3 15/16" in diameter. The height, measured from the engine block to the top of the plug wire boot is 9 3/8" for the 8350 and 8 5/8" for the 8577 and 6 7/8" for the stock Ford. So the 8350 is only 3/4" taller than the 8577.
I'm planning to run the 8577 and I hope it will fit under my 72 Pre L engine screen. I've read posts that say it will fit and others that say it won't fit. It will be a while until I install my engine as I'm in the process of preparing the engine bay. One thing's for sure, if the 8577 is a tight fit, the extra 3/4" height of the 8350 would probably not work. I'll post my findings when the engine is installed.