L34 spec heads are not difficult to have machined by your local machine shop, and affectively involve (its been a while since I moved away from working engines for a living so you'll want to check this info...) 1.9 inch dia inlet valves (1.94 rings a bigger bell, but you'll need to check) and about a 1.61 inch dia exhaust valves with some minor "throating" behind each of the valves which was flowed into a matched port (to the same size and shape apeture inlet or exhaust manifold). I cannot recall the size of the chamber but don't think we did much with them. Most of that will probably be on the YT (or similar) website anyway....
Most of the hp gains of a red motor are in the heads/valvetrain/inlet and header systems. You don't need a massive mother of a cam to get them cracking, they just need to breathe a little easier and the best way is to use components that will work together.
Roller rockers are not always better however they are most definately more suited to higher lift/longer endurance cams as they wont tend to want to rock slighly sideways on their fulcrum with higher lift.... They do a great job of reducing valvetrain temperature and friction however be aware some roller rocker installations will require that you change the rocker covers as they are too tall to fit underneath the standard covers. They usually come in a variety of ratios which will effectively mean that higher ratio rockers than standard (1.65:1 rings a bell here but again its been quite a while) will actuate the inlet and exhaust valves a few thou further (ie; opening the valve a little bit further) increasing the amount of potential airflow in and out of the heads as well.
Hope that helps.
Dave
[edit] starting to recall some of the jobs we did for different people.... I think from memory the big exhaust valve stuff was more suited to sustained high revs, especially for the seat temperature/way it scavenged the chamber. Dunno, you'd be better-off talking to a machine shop that has employees that have been around for 20+ years in the game.
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Having a look around at the Yella Terra website I'm not sure you can even get any parts for the red motor cast iron heads anymore.... Oh how times change....
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