This would make it very hard to check bearing clearances for the new rods, rod to block clearances, probably not possible to get the pistons past the journals and if you can you need to be careful of scratching the journals. Doubt it would be possible to get some sort of piston ring compressor under the crank to put the pistons in. The only way would be to pull the heads and at that point there is no reason not to pull the engine if you're going take it down to basically a bare block. Do it right or take it somewhere, its probably not the best idea to look for shortcuts on a 15K engine.