drive shaft help please

hello again guy and girls i am in need of help if possible .

i have had my engine in car using for a while now i decided to put the gear box in that was with the engine now .. i have taken the outer cv joint off the old shafts and fitted them onto the 20v shafts the passenger side went on and in no problem . came to the driver side again took the outer joint off the mk1 shaft and fitted it onto the 20v shaft went on no problem came to fit it in the car and its to long by about a inch … so i though ok il use old shaft so swapped the cv joing back over then i removed the inner joint off the mk1 then again on the 20v and went to put the 20v one onto the mk1 . wont fit  any ideas on what shaft people use for the O/S i have heard seat ibiza but what modle and year .. also my flange is the start shape one not your typical round one what makes things more complecated … any help would be much apriciated thank you veary much for any input 

oh sorry also the engine and gear box came from a a3 . if that helps .

You need to use the Mk1 100mm shafts and CV's. You will also need to change the gearbox cups to the 100mm ones.

keep hearing this 100 mm shafts .. how do you work this out ?    where do you take the measurement from its a 1983 1.8 gti tin top if that helps ? …

i have sourced a 20v engine and box from a seat ibiza cupra will this have the correct shaft and flange as stands my flanges are the early once apparently .  any way thank you for your replay . if could help me try to work out how i know if have 100 mm shafts or not would be good .

ok so i have heard a lot of ways tonight and yet no near to my answer as one person then contradicts what some body els said and becomes some chat about ways people have done cars in the days ect  

so i have sourced a ayp engine and box the box is still bolted to the engine and shafts came from a seat ibiza cupra 52 reg … i was told that ibiza once you would have to do nothing but change the flange and then bolts right in no daffodil about …

so can any body tell me if this is correct and if they do have the 100 mm flanges if so then that means the inner joint is the right one i need to so please can any body just say yeah or no to this :L not i need mk1 shafts transit van wheel bearings and transporter head lights  
     

im well aware of tools ect to on how to do the job its not a case of capability its a case of wanting to know what will or will not fit so i do not waste money and gain nothing but a bad head      

sorry but been a long day and got no where fast with this … and no doubt most common asked question but every one i have read is the same people saying different to the other person not relay knowing whats correct or not  

mine is a 1983 mk1 gti 1.8 tin top .dx originally if that helps with knowing what shafts mine are to  

the mk1 cab/rocco/caddy post-84 100mm shafts are what you want, the left shaft is actually the same as the mk2 but the right side is shorter on the mk1.

the ibiza cupra shafts are the same as mk2 golf so you do at least have one of the shafts you need

edit: 100mm measurement is the outside diameter of the inner CV joint