Have you looked at any online auctions? eBay has tons of 4 bolt main caps for those blocks you have sitting around.. around $10 for the caps and $5 for shipping. Yes, you'll probably have to get an align bore, but at least you'll use your 'free blocks.' If you do choose this route, make sure you get the correct timing chain, because the length will be slightly different. If you only taking your blocks (2 or 4 bolt) to the 400hp zone, everything should be fine. Just type [ 350 4 bolt ] and find a good seller.