[Will]

"... decent parts for the 350 are few and far between."

I beg to differ. The ONLY parts that are different between a 350 and a 400 are the pistons and rings. Absolutely everything else inside the engine is exactly the same and interchangeable.

It should not be hard at all to produce a 300-325 horse 350 with the heads, block, crank, and rods you have now.

Get the heads cleaned up and a good valve job put on them. See if you can get the head shop to put a back cut on the valves to remove the forging ridge and see if they will run a throat cutter into the bowls to open them up slightly above the top blend cut for the seats. Replace the guides if needed. Have the tops of the guides cut for viton oil seals. Chuck the metal spring "hats" in the trash. Install Crower 68404-16 valvesprings. Those springs will work fine at the stock installed height with stock retainers & locks and can easily handle any cam you're likely to put in this engine.

Have the pressed studs in the heads pulled and install 7/16" screw-in studs available from ARP.

Your stock rockers and pushrods will be fine if no signs of wear on them. If worn, toss and replace. Stock replacement pushrods will be fine, but I'd upgrade the rockers if your budget will allow. If not, stock replacement rockers with either poly locks (best bet) or big block Chevy crimp nuts will be fine.

Get the stock rods magnafluxed and checked for size on both the big and small ends. If they pass muster (not cracked or grossly out of round on the big end, good and round on the small end), have new ARP bolts installed in them and have them resized on the big end.

Have the crank magnafluxed and turned to whatever undersize it needs to be turned to. Don't worry about whatever that size turns out to be. Even .040" under on the mains is no big deal for the level of buildup you're doing. Buy bearings to match.

Buy stock replacement type Sealed Power cast pistons & rings for whatever overbore size you need to go to, up to .060" over.

Have the rotating assembly balanced.

Have the block decked so that piston-deck height is zero.

Install a Melling M54 DS oil pump & screen kit.

Install a cam with an intake duration within a few degrees of 210 @ .050" and a lobe separation angle between 110-112. I'd prefer the 110 LSA, making the Comp Cams XE256 a good bet.

Unless you really want to be different and "trick" I'd skip the whole TBI idea. There's no real advantages to that system and it just adds a level of cost and complexity that you will never see returned in performance. A custom built Q-jet can be had for $300 or less and will run every bit as good. You might sacrifice 1-2 MPG overall compared to a perfectly dialed in TBI, and unless it's a system that allows you to interface with a laptop and see what the A/F ratios are doing under every condition it'll never be "perfectly dialed in." Given the cost differential you'll have to drive a lot of miles to justify the extra cost of the TBI.

The money you save on the TBI could go to finding a 400 block to work with instead.

If you do give up the TBI, run a factory 4-bbl intake or an Edelbrock Performer topped with the abovementioned custom Q-jet.

Get some 1-5/8" 4-tube headers and plumb them into a 2.5" mandrel bent exhaust system, preferably with an X-crossover but with at least an H-crossover. A good pair of mufflers rounds out the system.

With distributor tuning and maybe a little carb tweaking (a custom Q-jet shouldn't need any real tuning), you'll have a very strong 350 at a cost close to $2000 for everything except the exhaust system.

If you have an auto trans, buy a Hughes GM25 converter. If you have anything numerically smaller than 3.23 rear gears, get some better gears in the rear.

Proceed to stomp Ford and ricer butt!