10checks.
It really doesn't matter as long as the B737-300 you're flying is EFIS equipped (which most are). EFIS is what most major airlines look for technically when assessing flying experience in a commercial environment.
Besides you already have hours on the NG so it wouldn't be an issue at all.
Stay current on an EFIS equipped commercial aircraft and there's no need to sweat about it!
All the best.