Without documentation, or the original engine with the partial VIN stamped on it, I am not aware of any way to pin it down exactly if multiple engines were a possibility. Hopefully you will be able to find something to show a L48 car.
CRG has documented SS and the various drivetrain variantations at http://www.camaros.org/diffs69.shtml
You didn't mention rear springs - does your ride have multi-leaf rear springs? Being a 12 bolt I am assuming that it does - which would be consistent for SS.
For Los Angeles 69 Camaro production, the last VIN # produced in November 68 was #510583 and for December 68 was #513816 (http://www.camaros.org/geninfo.shtml#HowMany
). Your VIN # 124379L512641
falls in between which would indicate Dec 1968 build.† What is the body build date on your cowl tag?†
Reason I ask is that if it turns out that your ride is a non-SS car, you may have to further evaluate the situation based on the fact that at the end of 1968, two non SS V8 engine changeovers occured:† LF7 to L14 (327 to 307 base variant) and LM1 to L65 (4 Bbl 350 to 2 Bbl 350).† The timing of both of these engine changeovers are open CRG items of interest.†
An issue fo Chevrolet Service News
from early 1969 indicates that the changeover from LM1 to L65 was to occur during Jan 69, but nothing definitive as to exact timing.† As far as the changeover in base V8 engines, it is hard to find any LF7's being built after Dec 1968.† In a previous request that I made to CRG regarding LF7 to L14 changeover, the data indicates that there are numerous L14s from 01A, 01B, 01C in the CRG database.† The last documented LF7 the CRG has is 12C, along with a couple of undocumented LF7s from 12D.†