Paulie, a couple of comments on this round
1 - Generally guys don't hog a TW out nowadays, however, who knows what guys did to "improve it" back when, it's worth checking to see if either hasn't been opened past medium riser. I will say though, a step on the bottom isn't a big deal, and honestly even a small one could live fine at that level of HP, but you could likely pretty easily knock down the top and side edges of the TFS head if required. I'd be less worried about making the port size work that dealing with a sloppy, really hogged out TW.
2 - You are planning a lot of cubes and a lot of cam, 550 hp shouldn't be difficult, and with the Trick Flows, my gut says, with proper parts choice, you'll easily beat that (likely significantly)
3 - Not sure when it will get on the pump given the CV-19 stop movement for us military guys, but I will be putting a TW, 295 cfm ported 457, with much less cam than you discussed (low 240s, but more lift), but should show you what the TW will do with a head about like yours now. I hope you'll be surprised
4 - I don't think just a stem diameter change and a little bowl/transition work is going to be dramatic to your Edelbrocks, unless the current valve job is crappy and the next one is good. It will help, but it's not going to gain you big numbers in my opinion.
5 - Don't forget, if you buy TFS for a solid cam, you will either have to buy bare and buy all components, or buy with springs and change them out, the supplied springs may work with a +.100 Ti retainer and some lock/shim games, but you'd likely start fighting with clearance issues and of course the setup time costs money too. Certainly just a WAG looking at the spring pressures, and springs aren't that expensive, but it does add to the cost
One thing I would consider is if selling both TWs and the Edels could pay for an unmolested MR dual plane and a portion of the Trick Flows? Given your effort to tame it down a little while making big inch power, might be a smart move if the numbers work
In the end though, a healthy 474 inch engine, shouldn't be too hard to hit 550 hp. We just jammed my truck motor at 13 less cubes, 9.75:1, and a Comp 280/230 HFT and 277 cfm truck heads at 490 hp with zero tuning. Add cubes, compression, cam and airflow....you know the drill