Howdy Falcon Fanatic:
The two choices on lighter, swap-in one piece retainers are OEM retainers from earliy 221 and 260 V8s, @ 24 grm. Part # was C3 428514-B. They are very scarce due to the smaller diameter 5/16" valve stem, necessary to be compatible with our six cylinder valve locks.
The other choice is one piece retainers from a 4.0 V6. They weigh in at 23 grams and should be available from your local Ford Parts window. The part # is E6TZ 64536-A. The are quite pricy.
In addition to the lighter, one piece retainers, be sure to add a back cut to the port side of the intake valves. This lightens the valves and gives the effect of quicker opening and latter closing, and more lift.
Be sure to add a three angle performance valve seat. Milling the head not only raises compression, but it drops the valve slightly deeper into the cylinder for slightly less shrouding. Also shimming the stock springs up .030" is cheap and good for a little more valve control.
This is also the time to get, fit and install an exhaust port divider.
I would encourage you to heed Wsa111's advice, and consider a cam upgrade. As long as you're going to the trouble and expense of a head rebuild, spending a little (well, more than a little) on a better cam and a new double roller timing chain and gear set is worth it. Mike has the right stuff and very competetive prices.
Adios, David