It's not really solid rollers that make cams less streetable, though many will tell you that they do require more maintenance than hydros (checking lash, and adjustments, periodically). It seems to me that it's the high-revving aspect that makes cams less streetable. High overlap, long duration, short LSA cams seem to pull less vacuum and lope harder around idle speeds. I'm not saying what you should or shouldn't do with your car, but if I were building a streetable fun car, it would not have such a cam in it.
I told you that I'm the wrong guy when it comes to 351 advice, but I'll give it a shot. I suspect that 200cc heads would be fine at 351 actual cubes, but if you went to a 408 stroker, they'd probably be a pretty tight fit, especially if you're planning to rev it. You could still get away with them for a lower RPM street car. No comment on the budget part, as I've never done it.
About the R blocks: I've never heard of one breaking due to power alone. You'd be a bad MFer to split one of those on power alone.
Now it seems to me you're changing your story a little. Here you say 400-500 rwhp is all you want, and in that case, keep your stocker and stroke it out. That's a realistic possibility with the stocker and you'll be able to run that power safely. Going beyond that 500 rwhp mark is hazardous with the stock block, though. Earlier when you were talking about 300 shots of nitrous and 600-700 rwhp, the recommendation for such a combo was the aftermarket 302 block or a 351W block, and the recommendation was appropriate for those circumstances. Here's some general advice: if you're not sure where you're going to end up, do it right once rather than wrong several times. That way you'll end up with more, sooner, and with less long-term expense.
Do not spin a stock blocked 302 or stroker variant to the 7500-8000 rpm range. They will not take this kind of abuse. I know of a guy who, with a neutral balanced rotating assembly, was unable to spin the stocker to 7800 rpm without crank-walk. He had severe problems with stock rotating assembly taking it to 7300 rpm. He was turning damn good times for what it was, though.
Hope some of this helps,
Chris
yeah, that guy had one hell of a fox. ive watched his videos so many times and im still not sick of them. As for what block, ive been lookin into the R block but if i found a good deal on a dart or boss i would go for it of course. im guessing the R is god for over 1000hp? anyone know? ive been to fords page but they dont put a rating on it. Going to say, maybe a 351 block i would have to change alot though right? like brackets, motor mounts, headers, intake would work if it had the same deck height as 302? but if i went that way i would probably have to get my RHS 200cc heads ported right? maybe sell them an get the 215s? i think goin the 351 route i would be changing to a budget thats to big for me. i mean i have my stock motor in the car but it would still take me most if not all of the summer to get all the parts, so it would be next year to put it in. so many options its rediculous lol. i want between 400-500 rwhp without it being a big hassle to drive on the street. i thought of a solid roller but huge cams like that dont make it to streetable. then again, i have always wanted to spin my motor up to about 7500-8000rpm so maybe now is the time to do it since the R block can handle it unlike the stocker.
Look at it like this I bought my 
It was a nice setup he had goin', though.
