Question about head swap
 

Would it make any sense to put a b18c5 head on a jdm b18c ? I know i will lose compression, but, if i used a thinner head gasket, would it justify the swap? or is it a complete waste of time?

i would say its a waste. Unless you mill the head and use a thinner gasket, but then you might have to worry about piston/valve clearance. A poor mans type R (its what its called when you put a b16/itr head on a gsr block) is good and has its benefits over a lsvtec, such as oil squirters, a block girdle, there's no need for an external vtec oil feed line and the vtec oil and water pumps already equipped on the gsr block. But in my opinion it would only be worth it if you put different pistons in. I would recommend civic type R pistons (pct) or at least jdm b16 (p30) pistons. PCT's in a gsr w/an unmilled pr3 head is about 11.7:1, now you can mill the head a bit or use a 2 layer OE gasket to get to 12:1.
Or if you mill the head like .030" and run the stock pistons you'd still have a decently high CR, enough to run some stage 2 cams.

so if i milled the head and used stock pistons would i make any gains? and how much?

yeah, you would probably see some gains, but i wouldn't expect much. IMO the gains wouldn't be worth the cost.

pretty much Im getting it for free, so Im wondering if it is worth me doing or not...........is it worth the hassle?

no, i don't think it would be worth the price of new head bolts (or head studs), head gasket, coolant and oil.