I too will second spreading the load across two if you can. Other-wise not knowing the particulars I could not say for sure... Generally speaking the lower portion of a truss is tension type load, (unless cantelevered) so long as you are not cutting material out you would be ok - but with a large lag you may be cutting material by installing it..... Generally a fastening method that disturbs the least material is the best. How 'bout a strut between two, over the top of the lower chord - then you'll only need a minimal fastener to hold it in place?
