You have some really serious issues. Transmission length being #1. Removing the center crossmember (cruciform) is really a tough assignment on an Alpine as it is the heart of the car. If it were to be replaced, a person would have to make up a jig to hold the car in proper alignment. I don't see any way this could be accomplished in kit form. If you insist on using this engine, I think it would be prudent to use a different transmission.
But moving into the engine compartment, some here (I'm leading the parade) do not consider an engine to be a "fit" if the firewall braces cannot be used. These are the braces that brace the firewall to the fenders. I don't believe it is necessary to use the stock braces, but something has to be used in order to hold the car in shape. I removed mine for several while the car was on a rotisserie. One side would not line up with the bolts, the other side, just barely. When it was installed the chassis pulled back into shape so the other side could be installed.
Exhaust. I have nothing to say on this issue as I have trouble visualizing in 3D.
You seem to be willing to consider to other engines. I can offer this info.
The GM 2.8 V6 family will fit the space with the usual exhaust problems. Barry has looked into the situation and while he says it is possible to use restrictive stock manifolds or fabricate a "shorty" header, he prefered to switch to R&P steering. As I understand his position, this was done mainly because he does not like the Alpine steering gear. The usual tunnel mods have to be made to use a T5. But I believe this engine has potential to be the basis of a kit.
Bill Atalla looked into the GM Ecotec and rejected it because of width problems at the front of the engine. He never explained this and I wonder if the problem is the block or accessories. In any event, I recommend contacting him to determine if the swap has any potential.
Bill decided to use the Ford Zetec engine. I think it has kit potential. It fits the space and the exhaust is on the correct side.
I installed a Ford Ranger 2.3 Duratec in my Alpine. I did this, thinking a kit could be offered, but decided no. It is a successful swap, but has these issues:
Intake and exhaust must be fabricated.
I had to relocate the alternator in order to fit a header. You might not, my header fabrication talents are nil.
The crossmember must be notched to clear the oil pump bulge in the pan.
The starter must be modified to clear the steering arm. An alternative would be to modify the steering location.
Exhaust is on the wrong side of the engine.
Oil pan is too deep, resulting in only 3 1/2" ground clearance. A new pan was fabricated, giving 5 + inches ground clearance.
Bill