To fully utilize the LS/VTEC, you need tp upgrade the rod bolts, which requires pulling the block out.
this^
hes asking about replacing or REbuilding, not building. he could do ls/vtec but it requres more than just a b16 head to function properly/to its full potential. the ls internals cant handle the rpms that a b16 head can, so it you would still be limited by the block, if he were to upgrade the internals then he could push it alittle further, but for it i woudl recomend forged high comp. pistons, forged/shot peened rods, all arp studs/rods, a block guard, and a bore n sleeve.
OP: i would get a new ls, they are cheap and it would be more expensive to rebuild it, you can get a good low milage or pre-rebuilt one for around 1-2k
it depends what you want though, if your looking for a swap to get more power there are many options, if you tell us what you goals are we can help you more.