one bit of advice I'd give _any_ first time cam swapper, is to deliberately go a bit conservative on the cam specs. Without a doubt as many as half the engine builds out there, even by guys with some experience, run a cam with too much duration and overlap and end up losing out on the mid range _big time_ and although the 'cam' will work at higher rpm, the rest of the combination, including the gearbox ratios that pull the rpms down lower than they realise and down and out of the powerband, just isn't suited to quite as much rpm and so instead of getting half the gains of the bigger cam, you get all of the low-mid rpm losses, and then because the rest of the combo is milder, you lose 'all' of the higher rpm potential of the big cam too.

Generally the wilder you go with a cam, aside from the rpm range going higher (if the rest of the engine spec will support it!) it also leads to a NARROWER powerband. This is the enemy of any street driven car, and frankly it's the enemy of a LOT of competition cars. Rallying is a good example of that. hillclimb to a lesser extent.

It's tough to know precisely what you are aiming at, but I'd make a strong case for the idea of not going for anything that needs to see the high side of 6000rpm for a streeter, and most of us here could make a good case for a lower limit too. Don't get me wrong, the engine itself will actually handle these sort of rpms if it's rebuilt properly, with new rod bolts (and nothing much more exotic beyond that) and all that, but it's not (at this stage) about whether or not you will break it but rather what the overall package will do for the car.

Another thing generally is that the wilder the cam, and the higher the rpm range, even 'with' a closer ratio gearbox, you'll still need to go with lower diff gears (higher numerical ratio) to get the thing to really perform. If the car isn't a true streeter and you aren't doing big trips on the highway that may just barely be liveable, but you tend to get sick (even if the motor will handle it) of a big 4cyl running pretty high rpms at cruise.

What you might consider doing in conjunction with this is locate a 5 speed gearbox, and running _slightly_ lower diff gears. For example if you are running 3.9s now, you could consider 4.11s and with a 5 speed the freeway rpm is still lower overall than 3.9s and a 4 speed, you could even go to 4.3s and the same would still (just) be true. That can help things potentially. Then again, the a15 has a fair bit more torque than an a12, so relatively you don't have to go quite as deep with the diff gearing anyway.

I don't know nearly enough about your engine to make any sort of an educated guess, but based on it being a streeter, possibly unported oval port head, and nfi what carburetion or exhaust, it'd generally be hard to suggest looking beyond around 250-255 degrees advertised duration.

It's also pretty important to know the cam specs before you machine the head surface at all. The thing is, there are compression ratios that are too high for any given pump fuel, and some that are ok. but it also depends on other factors. Being an alloy head, it'll tolerate more than a cast iron head safely, all else being equal. Being moderate bore size, also tends to help. If you could hypothetically run a head with a closed chamber, and a piston with a dish that matched the chamber 'bathtub' shape, that would tolerate more static comp ratio than an open chamber head and a flat top piston. And lastly, and of relevance to this thread, when the intake valve closes, also affects how much compression it'll safely tolerate. In general the 'bigger' the cam, the later the intake valve closure, and the more compression it can safely run. BUT it also 'needs' more compression to work well with a big cam, and you can get to a point where you just can't run enough compression safely to 'make' the cam work harmoniously. So with a basic plan of the overal combo worked out, you close in on the cam specs, and based on that, you can see how much you may be able to skim the head to bump up the compression ratio. It may actually be the case that you can't raise the comp much at all, due to a smaller cam, and (potentially) higher compression coming about fromt eh fact the head has been previously skimmed (as most used ones have by this point in time!) and or the deck of the block has been skimmed too. Even boring the engine oversize increases the comp ratio, because the engine capacity is larger but you're squeezing that larger volume into the same chamber space at TDC.

I know this sounds like a truck load of info to absorb, but I assure you, picking a suitable cam and balancing the comp ratio to suit it (and re-curving the distributor to run the sort of advance curve such an engine will 'like') and you end up with a rock solid combination of parts that work very well together. Get one or more of these factors 'out of step' with the rest of the combination, and it can be a frustrating result.