Opinion, $10,000 isn't much for a built 500-wedge. Issues I have, are that it's doubtful that they would provide any sort of substance in terms of warranty work. Most of the time, it's you pulling the engine out and shipping it back. Verify if in the worst case scenario, what all costs are associated that you will be held accountable for. I would just have the shop also quote a short block build. Purchase your heads/cam/valve train separately, and have the shop install them (also degree cam) at an additional labor cost if that isn't something you're willing to do at home. Sometimes, you can come out ahead that way.
TF 270's on a 493 will make 625-650 HP with a very conservative build. That's reaching the near limits of the RB block. When you drive around in a 68' Charger, the last thing you want to tell someone is I have a small-block stroker. Looking at your current garage, i'm not sure you'll be impressed with the 'wow' factor. Just being realistic. In an a-body, my opinion would be completely different. A modern Hemi, such as the GEN III (5.7 eagle or 6.4 apache) would also make a great statement and offer excellent reliability/fuel economy with EFI. In a few years, that $4,000 investment won't even be in your mind. There will always be someone faster, just build for what you will enjoy.
There is no difference between cooling ability, and an RB with aluminum heads, intake, water pump, etc. will actually weigh near any stock small-block. In fact, a low-deck could actually weigh less than a stock small-block built with these parts. (ie: 360 - 550 lbs / 400 - 620 lbs base weight). 400 low-deck is also a world-beater with MW heads and 512 cubes, easily 700+ hp capable on pump gas. The block is a much better candidate for a performance build (knowing what we do now) than the RB.