I just looked at my 88 1500, it has the PS pump mounted on the drivers side in what appears to be the same location as the early mount holes. I can't see anything on the pass side though, too much stuff in the way. It could very well not be drilled out though. Numerous differences on the later engine, one piece main seal, different flywheel bolt pattern, no fuel pump location, center bolt rocker covers, different intake mounting holes, and others. I think they did some of this stuff just to complicate our lives. I have installed a number of GM crate engines (early design)and used the front mounts, I guess that's what I thought you were using.
Fred

Last edited by rfs56trk; 09/12/2014 9:29 PM.

1956 3100 Pickup/Red/350/3sp OD/PS/Disc Brakes
1957 Bel Air Sport Coupe/Red/355/TH350/PS/Disc Brakes
2017 Silverado LT Single Cab SB/Black/5.3/6 Speed Trans
1947 Willys CJ2A w/F-Head engine