Estimating RPM to RCF in Methods from Older Papers
I am not sure about what they used in 1958 (perhaps Sorvall). However you may look at recent papers for ECM protein isolation (if that was your objective).
Have a look at this article.
From materials and methods:

ECM protein isolation.
Fibroblasts or A431 cells were removed from the
surface of the culture plate with 2 mM EDTA in PBS for 3–5 min at
37⁰C. Detached cells were discarded, and remaining ECM proteins
attached to the surface of culture plates were washed with the same
solution. Cell removal was controlled under the microscope. After
cells were completely removed, matrix proteins were covered with 5%
acetic acid and incubated at 4⁰C overnight. Then, acetic acid was
removed and exchanged with a buffer containing 125 mM Tris-HCl, pH
6.8, 0.1% SDS, 10% glycerol, 1% DDT, 0.05 mM PMSF, protease inhibitor cocktail (Roche, Germany), and incubated at 37⁰C for 1 h. Proteins
were removed with a scraper. The procedure was repeated three times.
All protein extracts, including acetic acid, were combined and ECM
proteins were precipitated by five volumes of acetone. After
incubation at –20⁰C overnight and centrifugation at 7000 g for 15 min,
the protein pellets were dissolved in an appropriate buffer for
further analysis by one- or two-dimensional gel electrophoresis.
In addition, we obtained a Triton X-100-soluble fraction of ECM
proteins. Cells were removed as described above; dishes were filled
with 1% Triton X-100 and incubated at 37⁰C for 30 min. The extraction
was repeated three times. The following procedure of ECM extraction
was the same as described above. Samples obtained from both fractions
were dissolved in a buffer for one-dimensional (Laemmli) or
two-dimensional (rehydration buffer containing 8 M urea, 2% CHAPS, 20
mM DDT, 0.1% Triton X-100) electrophoresis. Proteins that remained
after Triton X-100 extraction were dissolved in Laemmli sample buffer.