IMO, I'd do the ls swap now.
its easier to add a head to a block, then it is to pull it all out, build it, and put it all back in again.
hell do it all at once. you can build an ls vtec out of a b18a and an sir head/sir tranny for under 2k easily.
by the complete ls swap from a junkyard, buy an sir head/im/computer off ebay or the classfieds for 4-600 bucks.
sell the ls tranny, buy an sir tranny.. ends up costing you 250 or somethign tops. done.