Hi Andy,
Its Steve with the VI!
The IV looks class mate, immaculate aswell. Like you say, get a V/VI block fired in there. If your going down the 2.3 stroker route mate, 320hp will be nothing, although big money as it'll need forged pistons/rods/stroker crank, a rebore and then other adjoining mods to run efficiently. If your not intending on over 400, id just think about getting a later block, and dropping IX pistons and rods in, should be good for 400/400 and much less money.
Il have pop round over the weekend for a crack pal, got a few new things on the VI now aswell