What valve springs should i choose?

[blykins]

Unfortunately, install height is not always the exact same between intake and exhaust valves. One valve may be shorter than the other....one valve may receive a different angle valve job than the other, etc. You should always check between the two.

You are correct in that the exhaust valve is lighter and thus doesn't need as much spring pressure. However, that side is not one to be experimenting with, as if your exhaust valve floats, there's a very good chance that it will contact the piston as it's coming up and the end of the exhaust stroke.

If I were in your situation, I would measure each install height, calculate what you want your open/seat pressures to be, lay your shims out for each valve, then assemble.