I have made 3 kinds of Distributor hole plugs. The standard if you just need to seal up the hole for a distributorless ignition system. The -8AN or -10AN can be used for a turbo drain or breather port. The breather models have been machined with access for a 1/2" ratchet so you can tighten your AN hardware.
$30 -10 or -8
$20 Standard
$5.50 Shipping in the states
$17 Shipping international