4A-FE vs 7A-FE

Hello. As background information, I live in Finland so all cars is question are European Spec.

I'm thinking of upgrading my 4A-FE (from 1993 Carina E, same as the one from Corolla AE100, with Denso distributor) with bottom end from 1998 Avensis AT221. Basicly making Celica AT200 7A-FE engine on tight budget.
Carina E 7A-FE would also be available, but they are Lean Burn engines so they have different heads as they have flaps in intake. I don't know if old style intake would even fit and is the head flowing as good as older one?

Can 4A-FE ECU control increased capacity correctly or do I have to find AT200 Celica ECU? Are injectors with same resistance and do they fit or do I have to find Celica injectors too? 

How about camshaft profiles and combustion chambers in pistons and heads, basicly how much does compression ratio change and do valves have enough room to open correctly?

Celica Carina and Avensis have different part numbers for pistons. Conrods are same between Avensis and Carina E 7A-FE but not the same in Celica. You have to use 7A-FE pistons as piston pin is 2mm larger than 4A-FE pin.

You cannot use Avensis head as it does not have place for distributor.

AT200 7A-FE head is the same part number as 4A-FE Carina E head.

Problem is that AT200 Celica engines are hard to find and expensive in Finland, but Avensis wrecks are found everywhere and cost almost nothing.

So my question is basicly if difference between Carina 4A-FE and Avensis 7A-FE is made mechanically by changing port/valve sizes and angles and/or camshaft profiles/lift in the head to reduce emissions and lower power or is it all made electrically in ECU and with intake and exhaust profiles?

And yes, 7A-GE would be nice but idea is to retain 4A-FE stock engine management and keep the car "daily driven". I have multiple 4A-FE heads but no 7A-FE bottom ends, I would like to know which one I have to find. I'm thinking about few different engines so this information is for future build.