i don't mean to be rude or anything, but it's going to cost you a lot more than you think it will. as many have said in this thread, you will need a bucketload of money to carry out the work and of course it will have poor re-sale value. i was thinking of doing the same thing but was advised not to by somebody who actually did do the swap and the conversion in the end, which he said was a regret. plus, you are not going to get cheaper insurance just because it's a non turbo chassis, it's actually the same chassis used by the 25GT-T. if i was you, i would just wait until the provisionals expire, and then invest in a clean R34 25GT-T which will be cheaper than the actual cost of making an N/A R34 a stock R34 25GT-T.
if you're going to mod, just do basic things like exhaust, wheels, etc but try and keep it as stock as possible (even if you keep the OEM parts and whack em on when you're selling, you will retain the cars original value and not lose too much, don't forget.. another p plater WILL pay $14500-$15000 for an R34 25GT that has been looked after well and cared for)
my two cents.