Max lift with stock valve length?

It's time to start putting my '71 340 back together so it will be ready when the body/chassis work is done. Might not make sense but I'm doing an iterative build over time with different cam/head/intake/carb combinations in hopefully increasing levels of HP. I'm retiring and an ongoing project like this will help keep me out of the bars during the winter. I will be doing the majority of the work myself and I hope to learn from success and failure.

I want to start off with the stock 2.02" J-heads that were on the motor. They look to be pretty low mileage but I'll go through them and make sure the guides are good, etc. I'll be porting the heads myself and will freshen up the valve job. It was running a stock 340 cam, but I will be starting out with a solid flat tappet cam that is 242/247 @.050", .540"/.549" lift, and 109 lobe separation. With the correct head prep to lower the seal seats, will the stock length valves support this amount of lift? Springs appropriate for the cam will be purchased, maybe I need to figure out what those are first so I have the setup specs? I'm not against going to a longer valve, but to get the project rolling, I would prefer to use what I have.