First of all, is the car manual or auto? If it is auto then I would suggest going for a manual conversion straight away. You won't believe the amount of difference it will make over an auto EA.
Then I would just look at things like Extractors and an Exhaust upgrade. Then maybe a Chip and Cam as well. All of these mods won't break the bank and will give you a pretty quick EA.
This is just my opinion, but I wouldn't bother with the V8 idea. You'd be better off spending money on the six because the cost involved in putting a V8 into an EA will be quite high. With the equivalent money spent on the 3.9 you will be eating many V8s for breakfast anyway.
Hope this helps...