Usable power for the street?

The 273 would be more original for that car. A tighter LCA cam with high lift would be the answer. Use David Vizard's formula for determining LCA.
LCA = 128 - (CID/#cylinders/[valve diameter × .91]). There are some "factors" that can be applied to tune the LCA like CR. Watch his Powertek 10 videos on Youtube or get a copy of his How to Build HP book.
Physically the external dimensions of the 360 are pretty much the same, so use what is available and easily attainable for you. Depends on your street definition. A search in parts books and comparing dimensions can provide slightly larger valves to aid low lift flow. At less than 0.350" lift (give or take) the valve curtain area is the flow limiter. This is the seat outer diameter (head dia x .91) x pie x lift. Above that the port becomes the limiting factor. So for a mild performance build, a bigger intake valve is a benefit. When the exhaust valve opens there is still 70PSI to 100PSI left in the cylinder, that pushes supersonic exhaust out past the valve. So this is not as critical.
For the 1966 289 in my 1940 Ford, I am installing the Chevy LS 1.9I, 1.55E valves. Stem length is about the same. Guys have been installing the 1.94 Chevy valves for years. The LS use a 8mm stem instead of the 11/32" small block Ford and Chevy size. My heads had beenn done once and the guides knurled. The machinist will be putting 5/16" guides in and hone to the 8mm. This way he can fine tune the stem clearance. The older 289 heads had a spring installed height of 1.64" while newer are in the 1.8". Mod motors use a spring with the right installed height. TFS sells PAC springs with the 1.64" installed height and good for 0.550" lift. Just need the retainers that fit the 8mm stems and the top of the beehive valves.
Seems the newer Hemis use a small dia stem also.