You can start with any viable 350, 4-bolt block. You're more likely to find those in trucks. The only distinguishing feature of the Y-Body L-98 is the aluminum heads. Those are going to be the most difficult to find for an authentic rebuild.
However, the 1985-86 Corvette L-98 would not be my first choice as a starting point for various reasons:
- While the factory aluminum heads are a slight improvement over their iron siblings, the aftermarket has far superior heads available for reasonable prices.
- With the reformulation of engine oils and subsequent removal of EP antifriction additives, I would no longer consider building any replacement engine without a roller cam and lifters. Because of that, and the fact that the GM factory design roller lifter system is not only adequate for higher lift and RPM operation, but is the most cost effective system, it may be better to begin with a 1987 or later 350 block already incorporating a roller lifter system.
- While the Y-Car and many truck SBCs were equipped with 4-bolt main bearing caps, they were straight outer bolts. For the greatest strength of the lower case, begin with a 2-bolt main case and machine it for 4-bolt main caps with splayed outer bolts.
Everything else is equal. A good pair of aluminum heads, improved dual pattern cam, and stout rotating assembly in a prepared 2-bolt block might cut into your wallet for almost $2000 with all the necessary parts. That will depend upon how much machining, preparation, and assembly you perform and how much is farmed out. By comparison, a prepared short block can be had for around the same price:
http://www.sdparts.com/product/12561...eAssembly.aspx