A modern mechanical cam and springs requires what work on the heads?

Have a 1965, 273 commando. Previous owner swapped the mechanical cam, lifters and rockers to hydralic and put a 340 cam in it. He did not change the springs, though. I'm plying with the thought of swapping it back to mechanical since my friend have mechanical rockers, rockershafts and pushrods on the shelf. Then go for a modern mechanical cam and springs. Before going into what cam to get. "Moper" wrote earlier in another thread:

"Factory type seals are too wide for the dual springs modern cams need. The seal wont fit in the spring. So you have to cut the guide smaller in diameter. The stock retainer will hit somewhere around .520 or so depending on the engine so at the same time you make the guide shorter. Also, the spring won't fit in the spring seat on the head. You have to cut the spring seats for the inner spring too."

So this means that with any modern cam, I have to pull the heads and get them to a machine shop? This is whats put me of the idea a bit. Since this is to be done on the cheap side or else I'll just be happy with what I have now. It would be fun though to run it with a more radical mechanical cam

This is the setup today:
273 Commando - 1965
Cam: 268/276 duration and 429/444 lift
Edelbrock D4B intake / Edelbrock 600 Performer Carb
Pertronix Ignitor
Hooker Headers
2.5" Dual Exhaust / Flowmaster Super 44
727 auto / Shift Kit
10" 4000 stall TCI converter
8 3/4 - 3.55 - SureGrip