Im doing a similar project right now, I'm working on an 82' cutlass supreme with a 355 sbc. I was ust wundering what the current status of the engine is. Is it still all together or is it taken apart, do you have the heads off yet, if so, what kinda pistons are in it. If they are dish tops, you will have a hard time getting 100 more horses outta them unless you find some really small chamber heads to boost your compression. Basically you possibilities are endless, It just depends on what you wanna do with it and how much you wanna spend. Like Jim said.
If its got flat tops in the short block, and you know the rotating assembly is good, I personally would leave the short block alone to keep the budget reasonable. you can get 300 HP outta that short block quite easily. Just get a decent cam and some good heads, intake, headers, and carb, and you should be atleast to 300, probably well over.
Check out this article, they basically started with a junkyard block, punched it .030 to a 355 and threw in some forged dual 2 valve relief pistons and managed to exceed 500 HP with the right combo.
Please correct me if i'm wrong, but that is a roller block right?? I'm not really familiar with the new ones my SBC's are all pre 86' so they are a little different. I'd say you could pretty easily go with one of the matched engine kits like the Holley systemax kit, edelbrock topend kit, brodix kit, dart kit, Im not sure if AFR has a kit or not, but i'd say anyof these kits will put you well over 300 HP with flat tops with 64cc heads. You could always have someone help you match your own kit also, but these are dyno tested HP/TQ why guess if you don't hafta. Please provide more info when you can, and be sure to read that article, Its very interesting, to know that you can add 250 HP with a comp XE294 and some AFR 195's CNCed.