302 heads for 318

You've got the right idea. Everything can work just fine, but I agree with keeping it all in one swap, though.

The primary barrels on the carb I went with are smaller than the 2bbl carter that was on the Scamp.

I eneded up rebuilding the low end, because I discovered the factory cam was trashed from new oil (no phosphorous).

The cam that Rob suggested from Summit looks like a bump up from a stock 340 cam, with a good split duration for full exhaust like you have.

The one I'm running is a .461/.489 with a quick ramp and puts the cam right where the limits of those heads are at, without cutting the guide seats for more retainer to stem seal clearance, so that Summit cam should work great with a new set of lifters and correct springs.

All together, I think I've got about a $1300 in the top end of the motor, with the carb, intake, what the cam set is currently going for and heads with valves are going for.

I spent some money on pistons and machine work. I got the heads for free and I had the cam sitting for another engine build for years, so it wasn't as much out of pocket.

I think you should get the parts as you can afford them and get them all ready to do the top end of the engine.

Just out of curiousity, what oil are you running? I haven't found a decent oil that isnt chalked full of extremely high levels of detergent, suitable enough for any ZDDP additives. I'm running Brad Penn's Penn Grade.