i would take the heads to a machine shop, get the O.D. of the top of the guide cut smaller, and put positive locking seals on. they are the best. i changes my umbella seals once, and the car still smoked after. after i did the locking seals, i could go 3000 miles and not have to add a drop of iol, even beating on it.
but if you dont want to do that, a local machine shop, or summit has the regular umbrella seals that should work fine.