Dave,
For 3k your not going to get much...
The STD N42 head flows 'ok', so I would be just looking at match porting the head to the manifold.
Go the Webers if you don't mind higher fuel consumption & slightly rougher running down low in the rev range.
Try & get a set of extractors (if you don't already have a set).
A MILD camshaft & new lash-pads & heavier duty valve springs would also be an excellent decision.
As the the N42 head has large chambers, I'd look at a set of standard style flat top pistons to raise the CR a bit.
And at the end of all this, budget $600 for a PROPER session on a rolling road dyno, to set the tune.
I recommend: http://www.powerplay.net.au/
Pauly, unless the Rev. has 5k+ to spend on the conversion & the budget to maintain a L28et engine, this is NOT an option.