What is the maximum lift that can be used with these heads. they have screw in studs but not sure what the springs are rated at, so im going to stay in the stock rated area and find a cam to match.

it'd be a dumb move to keep the unknown springs when you can replace them with springs to match your cam for cheap, trash the stock rotators and retainers too and go aftermarket

Your max lift is restricted more by coil bind of your valve springs. Best bet is to get the springs your cam company recommends.

461 heads are not that great anymore with all the good aftermarket heads available. The 461 came with 2.02/1.60 valves but the intake ports are a tiny 165cc. They also don't have accessory bolt holes in them.

All production heads are cut for 1.250" diameter springs. Even the best springs this small only get about 120# seat pressure. Typically it's only 80#. To be able to use more seat pressure and lifts greater than .480 (usually max lift with stock springs), you need to have the seats cut for 1.460" springs.

Although they already have screw-in studs, if there's no other machine work done to the heads, it will be cheaper to buy some Dart heads. Once you cut the spring pockets, new guides, new valve seats it'll cost you more for 30 year old castings than a set of new heads that will be better right out of the box.

Wait wait, people are finally starting to figure this out?! Tell the world!