400+ HP and 500+ TQ is certainly not unreasonable for a TBI setup. I have a very mild setup in my truck, making about 300HP and 400TQ (at the flywheel). 400 LB-FT of FW-TQ will turn anything into a blast to drive, especially a light 2WD RCSB, and you'll have plenty of grunt to pull loads, one of the best things about a TBI setup. Off the shelf chips and mail order tunes are MARGINALLY better than a stock tune, at the best. If you want to get the most power out of any TBI setup you must tune it yourself, b/c it is a long, drawn out and time consuming process. The reason for this is the 7747 ECM is probably the most primitive ECM out there and the data update is 160-baud rate. In plain english, this means that you're only getting input from the ECM every few seconds, which by today's standards is sloooooow. All this means however is that tuning takes longer, as there ends up being more 'educated-guesswork' to fill in the gaps. If you're planning on sticking with TBI, then I would recommend DynamicEFI, which is an upgraded daughter-board for the TBI ECM. This upgrade makes tuning MUCH easier, and you get more data to work with in the same time period for tuning, it has Auto-learn VE (Fuel table) functions which is very nice.
In terms of hardparts you can still build a brick-*********-tough TBI even w/o tuning it. However, a tune is always going to bring out the most of any combination. These things MUST be addressed:
1.) Replace the entire exhaust system from the manifolds to the tailpipe, the factory exhaust system is EXTREMELY restrictive.
2.) Ditch the factory cam, the factory TBI cams are PUNY. There are a bunch of cams that would be better than the stock cam, so the choice is yours, I'm running the Elgin duplicate grind of the Crane 2030 which cost only $50 compared to the Crane's $200.
3.)Ultimate TBI mods
4.) Port and polish the TBI (swirlport) heads. If you have money for aftermarket heads go that route, but the TBI heads have long gotten a bad rap for no good reason. IF you port and polish them they will perform superbly from idle-5,000 RPM. Great cylinder heads for a pickup.
5.)Tune
The stock bottom end will be fine as long as you're not constantly revving it up to 8,000 RPM