Apologies to PHJ426. I went back and reread his original questions and noticed that he had latter stated his car had a 727. Totally missed that so my answers were really not to point.

So... IF you have the fab skills and equipment I would go T56. More gears to select from, better shift quality, shifter location in middle of trans hump gets rid of the foot well intrusion of the stock hump and probably just "feels" more correct (personal preference), more aftermarket support for upgrades/repair, much larger selection of clutches, shifters, flywheels and so forth. You are going to have to mod the tunnel sheet metal, fab an upper brace to tie the trans cross member back together and/or build a trans mount (I would do both). I believe you'll have to convert clutch actuation over to Hyd. Any questions on the T56 conversion I would ask 72Swinger as he's done it and is loving the results on the road and track.

As for the A855, fab effort is going to be much less. Cutting trans tunnel and welding in new hump. Installing clutch pedal assy. (bolt in), 4 speed carpet set. Most of the rest of the conversion requires the same but different applicable parts (bells, clutches, fly wheels, shifters, drive shaft mods et al.

Other than the fab work involved I would expect the cost comparison between the two would be very close.

Other things have to be considered, such as your rear axle ratio, which will affect the usefulness of six gears. May need to optimize that so add it to the cost if applicable. I think Jamie said the A855 has the same gear ratios as the 833 with the addition of an OD 5th gear. So if you liked those but were always looking for that next up shift then problem solved.

As for which is better for street and track: there are so few people who have driven a car with the A855 in it, other than Jamie himself, that the question is pure speculation and emotion at this point. Hopefully there are some getting seat time as we speak, er... type, so maybe some with 1st hand knowledge will be chirping in soon.