Just use the same flow rated injector the system was originally setup for assuming no fuel pressure modifications or fuel table modifications. Early small blocks typically used Kehien 26 lb/hr injectors at around 40-42 psi, big blocks stepped up the injector size to around 36-42 lb/hr at the same fuel pressure. You can get your existing injectors flow tested to see where they stand and will also tell you if they are flow balanced.

In short, IF you have say a 36 lb/hr injector, any other injector that flows 36 lb/hr will work with your system, assuming you can get the correct electrical connections and fuel rail/manifold fitting size.

thats because mercury never used the small injectors in this application, if the lb hour rating is the same on both injectors ( small & large ) buy Toms stuff and be done with it

https://www.ebay.com/itm/12367585652...3ABFBMkqiz_ppg

Don't know for sure, bought the MPI setup from a guy in NY many years ago, and the block is a Gen VI crate motor from GM at the same time.

My point is a MEFI 1 or 3 will work with the older injectors. Didn't know if you wanted to build more power or just keep it stock

I have a complete mpi set up including injectors id let go Bought it fora project and never completed it.
Has small injectors and the manifold is like new.

shoot me some photos. I messaged you.

Nice speaking to you on the phone. information for others who stumble acrossed this thread:
"early" 454/502 mpi efis used injectors that are called "honda Keihan style" they have a 11mm hole in fuel rail, no down legs on the rail and are about 2 3/4 long and the early intake used with them had a 22mm recess to seal the lower intake with a very large grommet, so a normal long style injector will not fit into the rail and would be loose with its 14mm od on bottom. strangely Mercruiser brought this EXACT injector back into service when they built the 525. It uses a EV-1 style plug and flows in the mid 40s lb wise depending if your testing with isoheptane or gasoline, 3 br pressure or less like these actually run
The later syle, mostly gen 6/mefi 3/cool fuel used a 14 mm od injector and it was about 1 3/4 long, the hole in lower intake is designed for 14mm end, not the huge grommet the early ones used. it was also rated in the mid 40s and had ev-1 connectors.
on a UN-modded 454/502 (no headers, no cam change etc) they run so rich from factory that many have swapped intakes and injectors as a whole with no issues from the slight differences in characteristics. I always recommend tuning based of tailpipe afrs if possible to be safe though, Smitty.

If you're still looking pm your phone number and Ill text you pics. Sorry I haven't been on this site since I replied and didn't see your pm.