I think you can get a pretty decent load with the right powders. I find on the Aks that I get pierced primers before I reach max loads especialy the 223. I recomend making a load up that is the hottest that can find run a mag through by string firing and recheck head space and recheck every so often with the normal lighter loads. watch out for bullets that are over size slightly as well. that will add pressure. I see some pretty decent loads that would IMOO be safe and are pretty fast compared to max loads that are often 10,000 PSI more. the short barrel you plan on using is going to make going to hot pointless any way as there likely will still be unburned powder. most of my guns shoot the best a grain or so under max anyways.
when kits were only $50 it was a very attractve to build a 308 or simular gun out of a AK kit but nw that there over $300 IMOO a Sagia cinversion is the better bet and it comes with a reciver and the correct bolt. I am collecting parts for a 22-250 fast twist barrel build that will be loaded lighter than the 65,000 PSI that those rounds can reach but it will still out run the 223 by a at least 250-300 fps with the heavier 70-80GR bullets I want to run. I want the case capacity needed to get the heavier bullets up to speed with lower pressure. theres a 6.5-300 savage wild cat in the works as well on a 2 lug trunion.
If you seriously have the machinery and skills and ability to properly machine and more importantly heat treat a bolt then simply make up a three lug bolt. it will fit in a staandard trunion. the 308 sagia is only slightly wider in the lug area or it would fit a Yugo trunion. while your at it make it longer in the front and then the barrel can be moved forward slightly. I think if a company or a individuale made some quality 3 lug bolts with big stems they would sell. I certanly would be interested in a few. If your not 1005 sure of the heat treat Id not attempt it. MY 50 BMG project is on hold untill I can get it dialed in. no gun is worth your face. the $500 or so for a used Sagia (I got mine for $350) is likley the better way to go I plan on loading my 260 remington conversion up to the max. I worry about the Saiga with three lugs holding. I havent heard of any coming apart the rest of the gun is crap as far as quality fit and finish and function. if it was some thing I didnt have a way to modify Id sell it. there very rough IMOO
good luck on the babby. hopefully in a bbout 10 years you can be fguring out how to do a 22 LR blow back for him or her.