hello.... yes, I did have a TH350 auto, and after getting it and converter rebuilt once, and then it needing doing again within a year I decided to go manual, as I was into driving it round corners more than drag racing so it was converted to a TKO about 5 years ago.
You'll need the pedal bar assembly as you know, crossmember needs replacing or modding (mine just a has a centre section cut and moved back/reversed to fit the TKO mount), clutch assembly and flywheel.
Mines hydraulic so also needed slave and master cylinders and pipework plus link rod from pedal to master cylinder.
The transmission tunnel wil need cutting/enlarging, and the console changing or modifying, plus a suitable set back shifter or it'll hit the dash when you change gear.
Also the propshaft will need shortening as the TKO is a bit longer.
Most of the work was done initially by Alders Automatics, who may know their stuff about auto boxes, but frankly did a bit of a rubbish job on mine as they'd never done it before and didn't admit they didn't have a clue at the time... most issues have been sorted now.
They used a TKO500 (same as 600, but slightly different ratios, and torque rating) as they got a Cobra TKO kit from Southern Roadcraft (
http://www.roadcraftuk.co.uk) as that's what they had in stock.
There were a few issues with this particular kit as it was designed for a Ford engine so had a Ford 10 spline input shaft, but with a Chevy bellhousing so it would fit my engine, hence my car now uses a Chevy pressure plate but a Ford disc.
Also they fitted the master cylinder flush to the bulkhead so the pressure angle to the pedal was all wrong, so it never worked properly, and the standard Sachs clutch could not take any power and slipped immediately as did the next 'uprated' replacement. (4 clutches later I'm now using McLeod RST twin plate which cope fine)
Also they cut the tunnel hole too small so the gearbox used to hit the body on acceleration.
If you go hydraulic you need an angled bracket to put the master cylinder at the right angle and mount higher up on the pedal to give more pressure, which I had made for mine, plus a smaller diameter cylinder for higher pressure. (if you look at the 4th gen master cylinder, the whole assembly actually mounts at an angle like this)
Total cost including their labour for the install and work, the initial gearbox kit, propshaft shortening, pedal assembly was a bit over £3k from memory...
Roadcraft have brand new TKO 600's in stock for around £1700, but you might find one cheaper here from another supplier, or get a 2nd hand one from US for less. So if you add all the bits it's still gonna be £2.5k +..
Once you've got a T10 installed it will be less as you won't have the actual manual conversion cost I guess.