900+ torque converter is dirt cheap.
If the converter is of decent quality, which it should to handle the 429 torque, it would cost at least 250 and likely more.
650 in labour is basically saying, they put it apart, most goes in wash machine and they change the frictions plates, o-rings.
I rebuild mine last year, also for a 429. Not all C6's are the same despite the common assumptions, the planets for instance, for a 429, they can have 5 rollers, 4 is fine and enough and likely what you have coming from a 70 Torino.
But there are must haves for a 429. The forward and direct clutches should have at least 4 frictions/steels. Some HP version even have 5. but a very large portions of the C6's are coming with 3. So I'd say, ask them to put 4 if there is 3, because behind a 429, that's 10k miles vs 100k if your right foot is on the heavy side.
They need to lathe 2 pressure plates to do this. The trick shops often do is to use another bottom plate and flip it. Nothing wrong on itself, but as I've seen and measured myself, you end up on the high side of specs, too loose (more wear and heat real quick). So ask them either to install thinner plates or better that they turn yours to end up with the optimal end play. If you have a true 70 trans, you might very well have the great larger drum that would allow 5 plates even if it came with 4. If thats the case, you should really ask that they push 5 in there. You'd have then a scj spec trans
I would also buy a shift kit, the C6 valve body is not that complex, and installing the shift kit in practice, is only to use the kit provided springs and replace the one valve that is under the body plate. One tiny hole in that plate is also required. An additional 2 minutes work for a pro. So there should be near zero extra cost for installing this shift kit aside the kit itself ofc, which is I believe 40ish.
Another additional detail if you have no lift at home: buy a new pan with a drain plug or weld a bung. The original messy way to drain oil is really unfriendly when you have your nose close to the pan bolts. Its a detail, but if your linkage would leak (common on cars that stay still often) and you need to replace that little seal, you will thank yourself for having that plug in!
Brands, raybestos, sonnax.. a full overhaul quality set is what you should ask for. They include servo, external regulator, clip rings for the governor and pump stator too.
EDIT: I would also make sure the converter they give you has a stall speed bits higher than the original. And make sure the crank pilot is the correct one. 9 out of 10 converters for c6's have the smaller pilot.
EDIT2: Check on your original converter, but I'm 99.99% sure crank pilot must be 1.850 in. While most C6 converters use a 1.375. Double check that one!
