Do that.

Go to JWS, get a complete STi long motor.. Put it in, GT30R swapover, and ENJOY.

Put your GT40R in the shed, and build a Cosworth 2.5 long motor with heads, crank and everything in between... plus dry sump.

Do it as you can afford it, then drop it in later

Sell your original pistons, rod and crank to recoup some funds.