Practically 1380cc or 1430cc is about as big as you want to take an A-series.....
1380 is a nice size and MED do some really good (Omega) pistons (73.5mm) which will take you to 1380cc with the standard crank.
If you up the compression to about 9.5:1 or 10:1 and get a decent gasflowed head with big valves then you should be able to turn 100 BHP with a FAIRLY docile ish cam.
Have a look at the spec of mine:
http://potteries.mmoc.org.uk/Members_Ca ... 9_1000.htm
http://potteries.mmoc.org.uk/Members_Ca ... engine.htm
You will definately need to replace the axle if you are pushing 100 BHP. I suspect that your car might still have the original axle as it will cope with the output of a standard 1275 and putting rear discs on it is total overkill for a standard tune 1275..... I suspect that it has front discs and rear drums......
Also watch the clutch too. It probably has a sierra plate, but a 1098 Minor clutch cover. If you uprate the power to 100 BHP then it will slip as the springs are not strong enough. You will then need to convert to a diaphragm clutch with a roller thrust bearing and a hydraulic clutch conversion will help matters too.
I have done all this to my car so if you have any specific questions fire away!!
