even if it would fit you'd lose acceleration with the longer ratios. top speed may be up a bit but it wouldnt be worth the loss of acceleration. whats the final drive ratio for both boxes? the gear ratios are relative to the final drive, multiplying the two together gives you a fair idea of how much easier or harder it will be for the engine to turn the gears.
in the past i've put different boxes on a few cars, both mine and friends, sometimes to see what a difference it makes to performance but usually because the old box was knackered and i couldnt get the same box to replace it with. on every occasion switching to shorter ratios improved acceleration and sometimes increased top speed too which doesnt make much sense to me but i guess the final drive on the box may have altered the speedo reading. going to longer ratios seems to slow cars down on acceleration and on lower powered cars sometimes decreases top speed too. i guess thats because the longer gearing is harder for the engine to turn so the engine doesnt have the torque to get up to high revs in 5th.
i ruined a 1.3 escort by putting a TD box on. it was as flat as a pancake. on the other hand i got the gearbox from a 1.1 escort and stuck it on a 1.6 orion ghia, that car flew, it beat xr3i's convincingly even tho they had the same engine and less weight. amazin what a change of ratios can do to a car. i've played with motorbike ratios by changing the sprocket sizes, a couple of teeth can make a big difference, it doesn't take much of a change in gear ratios to get a very noticable difference.
if i had a punto HGT i'd be trying to get a 6 speed sporting box stuck on, most probably impossible even with all the linkage. it wouldnt be easy stopping the wheels from spinning but once they stopped you'd be off like a bullet.
if you want to check if a gearbox will fit you could always go to a breakers and ask them to show you both boxes, if the bell housing matches it will probably fit with minimal fuss.
