Martin, I've recently been researching the internal/external balance question in preparation for buying a vortec crate motor and, while there's lots of discussion on the forums, most is confusing. to keep it simple I decided to go with GM's use of the terms when describing their crate motors. bottom line is that, for a 350 anyway, 1 piece rear seal engines are called externally balanced. 2 piece rear seal engines are referred to as internally balanced. it has to do with the small balancing flange on the flywheel/flexplate end of the crank. this flange is missing on the 1 piece seal motor. apparently GM considers the flange to be part of the "internal" balance even though it is "outside" the seal and pan when assembled. the 1 piece crank requires the balancing to be on the flywheel/flexplate. thus "external" balance
lots of starters come drilled with 4 bolt holes to fit either diameter wheel. btw, for future reference, you don't have to count all those teeth, the 168 tooth wheel will be 14 inches in diameter, the 153 tooth is 12 3/4" IIRC
also, from the mortec site (
http://www.mortec.com/castnum.htm): "14093638...350...87-95...2 or 4...Roller or flat tappet cam, one-piece rear seal"
I don't think that's a "vortec" try checking the cylinder head casting number