I wouldn't be too eager to swap the cam on your donor 318 unless it's a factory roller motor as 1985 is the first year of that feature and there's a chance it could still be flat-tappet. If it is roller you could reuse the stock roller lifters and just need to get a camshaft and valve springs. There are more than a few reported issues with aftermarket hydraulic flat tappets/lifters these days having poor machining and causing failures that trash the entire engine, unless you pay extra for top-quality ones and/or know how to check new lifters to see if they're good to run.
Probably get the same or even better mileage too especially with an Edelbrock carb. I'd sell you the 600 cfm 1406 currently on the 360 in my truck but the throttle shaft bore in the base is worn pretty bad and makes a big vacuum leak. Tbh even "just" 200 hp would be over double what your smogger slant-6 currently makes. My D200 is heavier than your D150 and has 33" tires and even with a stock 2-bbl-cammed 360 with a 4-bbl and headers it has more than enough power to do all the truck stuff I need and can easily cruise at 80 MPH on the freeway, not that I'd recommend it. I totally understand wanting more power, I want to put a mild cam in this 360 but my '70 Duster is my go-fast vehicle. Just food for thought.
