serious street power.

I understand why you would leave the cam, carb, etc. alone for now. You want to just get the shortblock and upgrade the rest as you have cash.
I agree with Moper that you ain't got enuf scratch yet! Set your cash aside and wait for that next bonus.
Right now, I'd be concerned as to why it slowed down after you put on aluminum heads and whatever else you did. Maybe you could post what you had and what you did to it to slow it down.
I used to own a stock '72 340 Demon that I bracket-raced the bejeesus out of. On a grudge night, a guy asked me what was done to it, after we made a pass. He had cam, headers, carb, intake, etc., on his early small block Camaro and was embarrassed when he saw my "combo". What I'm getting at is; getting the most out of a combo is very gratifying.